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Labour Market Fact Sheet
Oligopsony and Monopsonistic Competition in Labor Markets
V. Bhaskar Alan Manning January 5, 2004 Ted To
Abstract We argue that models of oligopsony or monopsonistic competition provide insights and explanation for many empirical phenomena in labor markets. Using a simple model with job dierentiation and preference heterogeneity, we illustrate how such models can be employed to explain: the existence of wage dispersion, the persistence of labor market discrimination, market failures in the provision of training, and the anomalous employment eects of minimum wages.
The views expressed are not to be attributed to the Bureau of Labor Statistics or to the Department of Labor. We thank Alan Krueger, Michael Ransom, Dan Sullivan, Timothy Taylor, Randy Verbrugge and Mike Waldman for helpful comments and suggestions. V. Bhaskar is grateful to the Economic and Social Research Council, UK, for its support under research grant L138251029. V. Bhaskar is Professor of Economics, University of Essex, Colchester, United Kingdom. Alan Manning is Professor of Economics, and Researcher, Centre for Economic Performance, both at the London School of Economics, London, United Kingdom. Ted To is Research Economist, Bureau of Labor Statistics, Washington, District of Columbia, United States. Their e-mail addresses are vbhas@essex.ac.uk, A.Manning@lse.ac.uk and To T@bls.gov and their websites are http://privatewww.essex.ac.uk/vbhas, http://econ.lse.ac.uk/staff/amanning and http://Theo.To/, respectively.
Since its genesis in industrial organization and the theory of the rm, the assumption of imperfect competition has permeated many elds of economics ranging from international trade to macroeconomics to public nance. For example, in the 1980s, the introduction of product market imperfections revolutionized our understanding of trade policies and comparative advantage (Brander and Spencer, 1985; Krugman, 1979). At the same time, macroeconomists began to use models of monopolistic competition to explain how small costs of adjusting prices could give rise to business uctuations (Akerlof and Yellen, 1985; Blanchard and Kiyotaki, 1987; Mankiw, 1985). This trend is now inuencing labor economics, with a growing literature arguing that employers have some market power in the setting of wages. Indeed, the most common sources for market powerproduct dierentiation and imperfect informationseem to apply with equal if not greater force to labor markets as compared to product markets. The advantage of an approach based on oligopsony is that it leads to more plausible and less elaborate explanations of many labor market phenomena that are otherwise regarded as puzzles. This paper provides a brief survey of a number of areas where this approach has proved fruitful in recent years. One point should be claried at the outset. The question of whether a labor market is imperfectly competitive is often equated with the question of whether an employer is a monopsony in the traditional sensethat is, the sole employer in a labor market. Traditional monopsony is clearly unrealistic, since employers obviously compete with one another to some extent. But there are a range of choices between perfect competition and monopsony where a degree of market power coexists with competition between employers. It is best to think in terms of oligopsony or monopsonistic competition as the most accurate descriptions of the labor market we envisage. Oligopsony describes a situation where employer market power persists despite competition with other employersthe number of employers does not need to be small. Monopsonistic competition is oligopsony with free entry, so that employer prots are driven to zero.
The Law of One Wage
We begin with an empirical example that is dicult to explain using a competitive model. One key prediction of perfectly competitive labor markets is the law of one wage, which holds that there should be a single market wage for a given quality of worker. Even in goods markets with identical products, prices often vary. The existence of substantial wage dispersion among workers of very similar quality suggests that labor market imperfections are important and inevitably give employers some oligopsony power. A large empirical literature, dating back to the 1940s, nds evidence of substantial wage dispersion among workers that do the same job in the same city. The classic references are the case studies of Lester (1946), Reynolds (1951), and Slichter (1950). Although the data in these studies are now 50 years old, their conclusions probably remain valid today.
An informal telephone survey of fast food restaurants in Northern Virginia provides a clear and simple example of wage dispersion. The starting hourly wage among six restaurants surveyed, located within a circle of one-mile radius, ranged from $5.15 (the national minimum wage) up to $6.00 with a mean wage of $5.78. Contrary to the competitive theory of labor markets, these low-skilled, non-unionized workers are paid dierent wages by dierent employers. For a more formal illustration of wage dispersion, we consider the hourly wages of teenagers from the U.S. Current Population Survey for 19982000. After detrending wages, the teenager at the 90th percentile has an hourly wage 88 percent above the teenager at the 10th percentile. Of course, a portion of these dierentials results from dierences in personal characteristics, location and occupation. But, even after we control for gender, race, education, age, city, industry and occupation (a total of 903 dummy variables), substantial wage dispersion remains: the teenager at the 90th percentile still earns 63 percent more than the one at the 10th percentile. The problem with this evidence is that teenagers undoubtedly dier in ways that are unobserved by the researcher but are likely to be relevant in explaining wages. Perhaps the most pervasive explanation of this kind is unobserved ability as an explanation for apparent wage dispersion. Much empirical work in this area has focused on seeking controls for unobserved ability. For example, one focus is on the existence and size of industry-wage dierentialsthat is, whether workers of a given skill level are paid more in some industries than in others. Krueger and Summers (1988) and Gibbons and Katz (1992) provide evidence that the change in wages for an individual is related to the change in industry aliation. If we assume that an individuals unobserved ability is relatively constant over time, this provides an estimate of inter-industry wage dierentials that cannot be attributed to unobserved individual ability. Although Murphy and Topel (1987) and Keane (1993) contest this conclusion, they also nd some wage dispersion that cannot be explained. An alternative approach to demonstrating the existence of wage dispersion is to test predictions based on this view of labor market behavior. If wages are set purely according to productivity, then high-wage workers and low-wage workers will have little reason to quit jobs at dierent rates; after all, the highwage worker will just be moving to another job where high productivity leads to high wages, and the low-wage worker to another job where low productivity leads to low wages. But if considerable wage dispersion exists, then high-wage workers of a given skill level will be less likely to quit because they are less likely to nd a better job elsewhere. Conversely, lower-paid workers should be more active in seeking alternative jobs, because in a world of wage dispersion, they have a better chance that the next job, even at the same low skill level, will be substantially higher-paid. The evidence is in line with these predictions. A large established literature on the impact of wages on separation rates nds that higher wages, ceteris paribus, lead to lower quit rates (for example, Pencavel, 1972; Viscusi, 1980). Some estimates of the sensitivity of separations to wages from four data sets are presented in Table 1. For U.S. data, there is the Panel Survey of Income Dynam2
ics (PSID) and the National Longitudinal Survey of Youth (NLSY). For U.K. data, there is the British Household Panel Survey (BHPS) (which is roughly the British equivalent of the PSID) and the Labor Force Survey (LFS) (which is roughly the British equivalent of the U.S. Current Population Survey). The rst row of the table shows the mean separation rate, which varies according to the data set used. For U.S. youth in the NLSY data, 55 percent of workers leave jobs in a given year; for U.S adults in the PSID, 21 percent separate each year (the dierence is largely because the NLSY sample is younger). For the U.K. data sets, the separation rate appears much lower in the LFS because it is a quarterly rate, not an annual one. The next row of Table 1 reports the results of a regression where the dependent variable takes on the value of 0 if the individual has not left a job over the period and a value of 1 if the individual has left a job over the period. The row headed no controls uses the wage as an explanatory variable. Thus, in the PSID data a 10 percent increase in wages is associated with a 9.44 percent decrease in the separation rate. In all four data sets, higher wages signicantly reduce quit rates. The third row includes controls for education, race, marital status, children, region, experience, and year. The fourth row includes one more control variable, for length of job tenure. In all four data sets, the impact of wages on reducing separation rates remains substantial in magnitude and statistically signicant. Some economists doubt the importance of labor market imperfections because of high levels of labor turnover, which seems to imply an active and exible labor market. But, it is not the level of labor turnover that is important; it is the sensitivity to the wage. One reason that employers in eect face an upwardsloping supply curve for labor, rather than a horizontal supply curve for labor, is because a higher wage retains workers more eectively. Other evidence on this point comes from data on job search. The U.S. Current Population Survey does not contain information on job search by employed workers, but the British Labor Force Survey does. Some results are reported in Table 2. The rst two columns look at those searching for another job. The dependent variable is 0 if they are not searching for another job and 1 if they are. As shown in the bottom row, 6 to 7 percent of workers are looking for another job at any given time. The second column shows the coecient on wages as an explanatory variable; control variables for race, education, experience, job tenure, month, year, and region were also used, although the coecients are not shown in the table. The last two columns use as an explanatory variable number of search methods, the most common of which are going to the public employment service (more common in the United Kingdom than the United States), reading and responding to advertisements, and asking friends and relatives. Men and women as groups, including those who are not searching for jobs, use on average only about 0.220.26 of these methods, as shown in the bottom row (though, among those who do search, an average of about three methods is used). All the specications tell the same story. Those in higher-paid jobs are less likely to look for other jobs and to search less intensively (as measured by the 3
number of search methods) when they do. This nding is consistent with there being good jobs and bad jobs for workers with the same personal characteristics. Workers in the bad jobs devote a great deal of eort to searching for good jobs; workers in good jobs already have good jobs, so they search less hard. In addition, if low-paid workers face a greater risk of being laid-o, they will expend greater eort in searching for good jobs. Because one can always suggest factors that are dicult or impossible to observe or measure, it is dicult to rule out all alternative hypotheses and prove conclusively the existence of wage dispersion for similar workers. But a fair reading of the evidence suggests that wage dispersion among similar workers is a real phenomenon. This nding presents a signicant problem for the competitive framework. The alternative to perfect competition is to consider models in which employers have market power.
The Sources of Market Power
The model of the perfectly competitive labor market is based on the assumption that employees have a free and costless choice of a large number of employers for whom they might work. Competition among these employers then leads to a single market wage (or utility, if jobs dier in nonpecuniary aspects) for each type of worker. Any attempt by an employer to cut wages will cause all existing workers to leave the employer instantaneously. In other words, perfect competition implies that the wage elasticity of the labor supply curve facing an individual employer is innite. In contrast, with models of oligopsony or monopsonistic competition, the labor supply curve facing an individual rm is not perfectly elastic. The description of the perfectly competitive labor market itself suggests a number of reasons why labor supply might be less than perfectly elastic. The absence of perfect information on alternative possible jobs, as modeled in search models like Burdett and Mortensen (1998), is one reason; if workers must search for new jobs, a cut in wages will not result in the immediately resignation of all employees. Or it may be costly for workers to move between employers. Or workers may have heterogeneous preferences for dierent jobs; for example, a worker may have equal productivity in two jobs as measured by marginal revenue product, but the worker prefers the kind of work or working conditions in one job over the other. To keep the explanation simple we focus on this last possibility: we now sketch a model that focuses on the case of heterogeneous preferences. Suppose that workers with identical skills and abilities have heterogeneous preferences over nonwage job characteristics. Nonwage job characteristics include the job specication, hours of work, distance of the rm from the workers home, and the social environment in the workplace. For example, some workers are sociable and like meeting customers, while others are more retiring and prefer to work alone. Some workers nd the chopping of meat a brutal and odious business (Smith, 1776 [1976], book 1, chapter 10), while others may not have
such strong feelings and might instead have diculty in carrying heavy boxes. A teenager might prefer working at the local McDonalds over other low-paying jobs if friends also work there. A useful metaphor for heterogeneous preferences is in terms of the costs of travel to work (Hotelling, 1929; Salop, 1979). This notion of transportation cost can be interpreted literally as the actual cost of traveling to and from work. However, it can also be interpreted as a subjective measure of the extent to which a worker prefers one set of job characteristics over another set. Whether it involves physical distance or psychic distance, a worker may be willing to travel to the further, less preferred, employer for a sucient wage premium.1 The key insight here is that a worker in a preferred job may not immediately choose to leave an employer that slightly reduces its wage rate. To illustrate the idea of heterogeneous worker preferences concretely, consider the following model. Suppose that workers houses are uniformly distributed along a straight, mile-long stretch of road with rm 0 located at one end and rm 1 located at the other end. If workers incur a transportation cost of t for each mile they travel, then a worker located x miles from rm 0 incurs a cost of tx if she is employed by rm 0 and t(1 x) if she is employed by rm 1.2 Transportation costs give rise to heterogeneous preferenceswhether the worker prefers employer 0 or employer 1 and the intensity of this preference depends upon the workers location, x. Let us suppose that rm 0 oers wage w0 and rm 1 oers w1 .3 Figure 1 illustrates the workers situation. The horizontal axis represents the mile-long road on which workers live with employers 0 and 1 located at either end. The vertical axis measures workers utility, from workin this model, her wage net of transportation costs. A worker who lives at point 0 and works at rm 0 pays no transportation costs and will therefore receive a net utility of w0 . A worker who lives at location 1 and works for employer 0, will receive a net utility of only w0 t. For each worker located between 0 and 1, the line sloping down from left to right represents the net compensation for working for rm 0 at wage w0 . Similarly, the line sloping down from right to left represents the net utility for working for rm 1 at wage w1 . The marginal worker who is indierent between working for rm 0 and rm 1 is located at the point where the net compensation lines intersect, x . All workers to the left of x prefer to work for rm 0 and all workers to the right prefer to work for rm 1. Hence rm 0s labor supply is x and rm 1s labor supply is 1 x . Now suppose that rm 0 reduces its wage slightly, say from w0 to w0 . If
1 That is, a worker is willing to take a less preferred job if there is a sucient compensating dierential. The traditional theory of compensating dierentials is one of vertical job dierentiationsome jobs are good while other jobs are bad and wage dierentials compensate workers who take bad jobs. Ours is a theory of horizontal job dierentiationjobs are neither inherently good nor inherently bad, but workers preferences over them dier. 2 Since we are interested in heterogeneous preferences, it would be natural to assume that the cost of travel, t, is also heterogeneous over workers. For simplicity, we do not consider such extensions. 3 We assume that employers cannot oer dierent wages to dierent workers, depending upon their location.
rm 1 continues to pay w1 , rm 0 will lose some workers, since the point of intersection, x , shifts towards the left to x . However, it does not lose all its workers. In fact, its labor supply varies continuously with its wage rate. This is illustrated in the upward-sloping labor supply curves in Figure 2. If the transport cost parameter t is larger, the net utility curves will be steeper, and hence the elasticity of rm labor supply will be smaller. When an employer cannot oer dierent wages to dierent workers depending upon their location, a rm that wishes to hire more labor must not only oer higher wages to attract new employees but must also pay existing employees the same higher wage. As illustrated in Figure 2, this implies that the marginal cost of labor, M C0 , lies above the labor supply curve, LS0 . Firm 0 maximizes prots at the point where the marginal cost of labor is equal to the marginal revenue product of labor, 0 , hiring L workers. In order for L workers to be willing to 0 0 work for rm 0, it must pay them wage w0 , as determined by the labor supply curve. Because of the wedge between the labor supply curve and the marginal cost of labor to the rm, the marginal product of labor, 0 , is higher than the wage paid. If the labor supply curve for the employer were perfectly elastic, this gap would not exist. In general, the more inelastic the labor supply curve to the employer, the wider the gap between the marginal product of labor and the wage.4 Note that the labor supply curve faced by an individual rm (and thus the marginal cost of labor) depends on the wages oered by rival rms. In the basic travel cost example presented in Figure 1, the labor supply curve faced by an individual rm depends on the rival wage oered its sole competitor. What happens if the rival rm, which we will continue to call rm 1, raises its wages? The labor supply curve for our rm of interest, rm 0, shifts to the left and as a result, the marginal cost of labor to the employer also shifts to the left. This is illustrated in Figure 2 where following an increase in rm 1s wage, the labor supply faced by rm 0 shifts from LS0 to LS0 and marginal cost shifts from M C0 to M C0 .5 Again, the intersection of the marginal revenue product of labor with the marginal cost of labor will determine the prot-maximizing quantity of labor, and the labor supply curve will determine the wage that the rm needs to pay to hire that quantity of labor. This analysis demonstrates that rm 0 will nd it optimal to also raise its wages from w0 to w0 and reduce employment from L0 to L0 . The wage increase will not be as great as the rise in rm 1s wages. Furthermore, the rise in rival wages reduces rm 0s prots. Figure 3 graphs each rms optimal wage, as a function of the wage oered by its competitorthis is also sometimes called a rms reaction function. R0 maps rm 0s optimal wage as a best response to wages oered by rm 1.
basic formula is that the wage as a function of the marginal product of labor is given by: W = 1+ M PL where is the elasticity of the supply of labor to the employer with respect to the wage. 5 More generally, the labor supply of a rm may depend on all rival wages, some subset of them, or some aggregate measure of them such as the mean of rival wages. An increase in rival wages will generally reduce a rms prots by reducing its labor supply.
4 The
Similarly, R1 maps rm 1s optimal wage to wages oered by rm 0. Equilibrium in this labor market is given by the intersection of these reaction functions, R0 and R1 . Since we assume that both employers are equally productive, the equilibrium will be symmetric, with both employers oering the same wage. The equilibrium wage will be less than the marginal product of the worker. The greater the degree of preference heterogeneityor more generally, the greater the degree of imperfect competition in the labor marketthe greater will be the gap between the marginal revenue product and the wage. This situation need not imply that rms are making extra-normal prots. If there is free entry and exit and if xed costs matter in production, then any extra-normal prots will be competed away. Wages will equal the average product of labor, although they will be lower than marginal product. While this divergence between wages and marginal product has no immediate normative implication that workers are exploited, it does imply that, in general, market equilibrium need not be fully ecient.6 In consequence, redistributive policies such as a minimum wage, which would be distortionary in a competitive labor market, need not be necessarily so in an imperfectly competitive labor market. Employers have good reasons to try and wage discriminate, by oering higher wages to more choosy workers, because of the wedge between the marginal revenue product of the worker and the wage. In Figure 1, rm 0 could prot by oering higher wages to those workers who are located further away than x , while not altering the wage oered to its existing workers (those located to the left of x ). Such wage discrimination may not be feasibleafter all, location in our model is really a metaphor for a workers subjective preferences regarding nonwage job characteristics, many of which are not readily observable. Nevertheless, rms do appear to follow strategies similar to wage discrimination. Sometimes employers hiring workers will oer signing bonuses for new employees. Universities seem to bid more aggressively for outside professors, oering them higher salaries than equivalent existing faculty. Such wage discrimination strategies may increase the eciency of hiring decisions, although even perfect wage discrimination need not deliver full eciency (Bhaskar and To, 2001b).
What Empirical Findings Can Market Power Explain?
The theoretical arguments concerning imperfect competition in the labor market are largely straightforward and undisputed. However, the value of the oligopsony approach to labor markets must ultimately be judged by its use in understanding labor markets. Here, we suggest a number of areas where a model of labor market oligopsony has helped to improve understanding.
6 Indeed, as literature on monopolistic competition in product markets (Salop, 1979; Dixit and Stiglitz, 1977) demonstrates, market equilibrium need not be even constrained ecient.
Wage Dispersion
In a competitive labor market, employer characteristics should be irrelevant in the determination of wages, once one has adequately controlled for labor quality and non-wage aspects of the job. However, as mentioned earlier, there is considerable evidence that wages show consistent, signicant dierences across employers. Moreover, larger, more productive employers consistently pay higher wages, as do employers in certain industries. Oligopsony can explain wage dispersion easily. Let us return to our two-rm example, and suppose that the rms dier in their level of productivity so that, at every level of employment, rm 0s marginal revenue product is lower than rm 1s (perhaps due to the latters superior technology). Hence workers are less valuable for rm 0 than for rm 1, and its optimal wage, as a function of its rivals wage will be smaller than rm 1s optimal wage. This is shown in Figure 3, where the line labeled R0 represents rm 0s optimal wage when it has lower productivity. In equilibrium, rm 0 will set the lower wage and also have a smaller payroll than rm 1, although competition between the rms makes the wage dierential smaller than the productivity dierential. This demonstration, that equally able employees are paid dierent wages, holds quite generally for arbitrary numbers of employers and for arbitrary distributions over employer marginal products (Bhaskar and To, 2001c). Notice that the employer oering the higher wage also employs more workers. In Figure 1, w1 > w0 . If rm 0 oers wage w0 and rm 1 oers w1 then rm 0 employs fewer workers (that is, x < 1/2). This model thus provides a simple explanation for the well-documented positive relationship between wages and establishment size, recently reviewed by Idson and Oi (1999). Although the empirical correlation between employer sizes and wages is very robust, explaining it has proved surprisingly dicult. But since the employer size wage eect is a positive relationship between a price (the wage) and a quantity (employment), one of the rst (and simplest) hypotheses labor economists should consider is that it represents an upward-sloping labor supply curve to individual establishments. Here, as in other areas, oligopsony provides a simple and plausible explanation. Similarly, since the employer with higher productivity oers higher wages it must necessarily earn greater prots. Again, this is in line with the evidence that more protable employers tend to oer higher wages (Blanchower et al., 1996).
The Market Provision of General Training
The human capital approach to training suggests that workers should pay for the acquisition of general skills while employers should pay for the acquisition of rm-specic skills. In contrast, the oligopsony approach predicts that since workers are not paid their marginal product, they may not have sucient incentives to invest in training. In addition, employers may have an incentive to pay for general training because they can expect a return on this investment as they pay wages below marginal product and workers take time to nd other jobs (see
Stevens, 1994; Acemoglu and Pischke, 1999, for elaboration of this argument). This prediction is in line with the empirical evidence suggesting that rms do pay for general training they give their workers. As one example, it is not uncommon for business school students to have their tuition paid for by their employers. Indeed, Becker (1965) also pointed out that in an imperfect labor market, general skills come to have some rm-specic component. However, the ecient level of investment in skills is dicult to attain in this context because future employers of workers are also likely to appropriate some of the return on the investment as they pay wages below marginal product; however, it is dicult to identify and internalize these future employers in current decisionmaking about the level of training.
Racial Pay Gaps
Racial wage dierentials are very persistent. Altonji and Blank (1999) provide a comprehensive survey of the evidence and recent literature on this subject (see also the Journal of Economic Perspectives symposium in Spring 1998). Perfectly competitive labor markets should provide strong pressure against discrimination carried out by biased employers for several reasons. First, in a competitive labor market, a small number of discriminatory employers will have no eect upon the market wages of minority groups, since such groups can easily be absorbed by nondiscriminatory employers. Secondly, even if there are many discriminatory employers and this has eects on minority wages, the pressure imposed by competitive markets select in favor of nondiscriminating employers in the long run (Becker, 1957). In contrast, in oligopsonistic markets, even a small number of discriminatory employers can have signicant eects on minority wages, since dierent jobs are not perfect substitutes for each other. Furthermore, discrimination can persist and even enhance employer prots, rather than being competed away. Let us make the argument in the context of race, using our travel cost model. Suppose that white workers and black workers are identical in all respects. We assume that rm 1 is a prot maximizer, while rm 0 has discriminatory preferences, and suers a disutility d for each black employee. The optimal wage setting functions are depicted in Figure 3. Firm 1s optimal wage, as a function of rm 0s oered wage, will not dier between white and black workers; that is, its reaction function is identical for both types of workers. On the other hand, rm 0 will oer a lower wage to black workers as compared to white workers, that is, its reaction function for black workers (labeled R0 ) lies below its reaction function for white workers (labeled R0 ). In equilibrium, both rms will oer lower wages to black workers than white workers, although the wage dierential is lower in rm 1 than in rm 0. In other words, the prot-maximizing rm will optimally choose to pay black workers less, since discrimination reduces the alternative opportunities of black workers. What are the implications of discrimination upon equilibrium prots in rm 0? Clearly, the rm with discriminatory preferences (rm 0) will make less prot
than rm 1.7 However, discrimination by rm 0 could raise prots in both rms, provided that discriminatory preferences are not too extreme. Discrimination reduces the equilibrium wage of black workers paid by rm 1, and this raises rm 0s prots. This will oset the negative eect on rm 0s prots caused by its distorted (non-prot maximizing) choice of black wages, provided that such distortion is not too large. This insight implies that there is little incentive for a prot-maximizing entrepreneur to buy out the discriminatory rm 0a prot maximizer in place of rm 0 would drive up the wages of black workers in both rms, reducing both their prots!8
In a competitive labor market where workers are paid their marginal product, a minimum wage set above the market wage causes employment to fallworkers whose marginal products fall below the minimum wage will be let go. Recent empirical work has called into question this long-accepted belief. Card and Krueger (1995) oer a comprehensive discussion of this literature, including a review of many studies that suggest that minimum wages need not reduce employment and may in fact raise employment. The study that received the most attention (and also fostered the most controversy) was Card and Krueger (1994). They found that New Jerseys 1992 minimum wage increase did not result in a fall in fast-food employment and may even have resulted in an increase in New Jerseys employment relative to Pennsylvania (for a detailed critique of the study and a reply, see Neumark and Wascher, 2000; Card and Krueger, 2000). One of the reasons that Card and Krueger (1994) was initially met with skepticism was the lack of a convincing theory that could explain their results. Indeed, the discussion of minimum wages in any introductory course in economics concludes that a minimum wage must reduce employment. The fundamental question that must be asked is: How can a price oor lead to no decrease and possibly to an increase in quantity employed? While dicult to explain in the conventional competitive setting, Card and Kruegers ndings are easy to understand in an oligopsonistic labor market, even if there are many small employers and free entry and exit of employers. When rms have market powerdue to heterogeneous worker preferences, for exampleminimum wages cause changes in employment through two distinct channels: an oligopsony eect and an entry/exit eect. It is well known that a minimum wage can increase employment under monopsony (Stigler (1946) appears to have been the rst to demonstrate this). This is for the same reason that a price ceiling in a monopoly product market
7 The dierence in prots will be small unless discriminatory preferences are extremeby the envelope theorem the loss of prots suered by rm 0 is second order in the parameter d. 8 On the other hand, as is known in the literature on environmental externalities, if rm 1 (the prot maximizer) bought out rm 0, the wage setting externality would be internalized and both black and white workers would be paid equally low wages. While this possibility eliminates discrimination (at a depressed common wage), in a more general model with many employers, it is impractical.
can lead to an increase in outputa price ceiling prevents the monopolist from reducing output and raising price to the full extent that the monopolist desires. In the labor market, the argument is that a price oor like a minimum wage can prevent a prot-maximizing monopsonist from reducing the quantity of labor hired and cutting the wage as much as it desires. Without a minimum wage, the equilibrium wage and employment are shown by wi and Li in Figure 4. If minimum wage wm is imposed, the marginal cost of labor is now wm until employment reaches Li , after which it coincides with the original marginal cost of labor curve. Thus, the employer maximizes prot by employing Li workers so that employment rises by Li Li . However, a model with just a single, monopsonistic employer is rarely applicable in the real world. It is more likely that an oligopsonistic model would apply in the labor market, where multiple employers compete with one another for workers. Under oligopsony, our analysis of the eect of a minimum wage differs. In particular, if multiple employers compete for workers, the labor supply curve faced by rm i also depends on rival wage rates. Since rival employers must also increase their wage to the minimum, labor market competition increases so that the labor supply curve faced by rm i shifts to the left. This is illustrated in Figure 4 where the labor supply curve shifts to LSi and consequently the marginal cost of labor shifts to M Ci . The new prot maximizing level of employment occurs at Li . Despite the reduction in establishment level labor supply, a minimum wage set moderately above the market wage still causes establishment-level employment to increase because if all employers oer higher wages, the labor participation rate must also rise. Thus, even in the case of multiple employers, a minimum wage set moderately above the market wage can increase employment through greater labor market participation. Intuitively, by setting the minimum wage above the market wage, employers nd it easier to ll their vacancies. Of course, employers could have chosen to raise pay on their own, but to do so would cut into their prots, because payroll for inframarginal workers rises when wages increase.9 Notice also that because a binding minimum wage reduces employers prots when there is free entry into and exit out of the labor market, some employers will be forced to exit. Employer exit has a negative eect on total employment through the loss of exiting employer payrolls. That is, although establishments that remain after the imposition of a minimum wage increase their employment, some employers are forced out of business. Thus, minimum wages have two opposing eects: the employment increasing oligopsony eect and the employment reducing exit eect. The overall eect of a minimum wage depends on which eect dominates. In a more exible transportation cost model similar to the one here, the net eect has been shown to be positive (Bhaskar and To, 1999; Walsh, 2001). On the other hand, Bhaskar and To (2001a) set out a dierent model of worker preferences and nd
9 Notice that oligopsony provides an explanation for the persistence of vacancies, even in times of recession. Under oligopsony, employers are faced with a dilemmathey would like to hire more workers since the equilibrium wage rate is strictly less than marginal revenue product.
an unambiguously negative employment eect. The general conclusion that one should draw is therefore that a minimum wage set moderately above the market wage may have a positive eect or a negative eect on employment, but the size of this eect will generally be small because of the two countervailing forces. Indeed, even when employment falls, it is possible to show that the employment eect will be smaller under monopsonistic competition than under perfect competition. Under perfect competition, marginal revenue equals the wage (marginal cost), so that employment must fall with a minimum wage until marginal revenue rises to equal the new wage. Under monopsonistic competition, free entry implies that the average cost of labor (wage plus average xed cost) must equal the average revenue product of labor. With rm exit, average employment levels rise in surviving rms, reducing the average xed cost of labor. In consequence, the marginal revenue of the worker has to rise less, as compared to perfect competition. Hence, employment need not fall as much, and may even rise. This theoretical prediction is in line with the mixed evidence on the employment eect of minimum wages. Furthermore, these examples highlight one way in which oligopsony (or in this case, monopsonistic competition) diers from textbook monopsony. Under monopsony, a small enough rise in the minimum wage must raise employment. Under monopsonistic competition, it is possible that even the smallest rise in the minimum wage reduces employment.
Direct Evidence of Labor Market Power
The evidence discussed above in favor of the view that employers have some oligopsony power has all been indirect, comparing the predictions of perfect competition and oligopsony. But one can also take a more direct approach to measuring the labor market power of employers. The classic study of Bunting (1962), for example, examined whether wages are lower in labor markets with fewer employers. Little evidence for this is found, but this is actually a test of classic monopsony; oligopsonistic competition does not necessarily rely on large employers. For example, models which emphasize the costs of job search typically assume each employer is innitesimally small in relation to the market, so employer concentration is irrelevant. An alternative direct approach is to estimate the elasticity of the labor supply curve to an individual establishment. The literature on estimating supply curves to individual employers is small. This is in stark contrast to the voluminous literature on the labor demand curves of individual employersor on the supply of labor by individuals to the market as a whole.10 As noted earlier, one could interpret the numerous studies of the employersize wage eect as studies of the labor supply curve facing establishments. Boal
10 One might wonder how one reconciles oligopsony with the empirical evidence on the existence of labor demand curves; that is, if the employer is choosing a prot-maximizing point on a labor supply curve, then what does labor demand even look like? But, as the earlier discussion makes clear, we would observe a negative relationship between wages and employment if the elasticity of the labor supply curve facing the rm is constant.
(1995) takes this approach in a study about the elasticity in labor supply to coal mines in West Virginia in the early twentieth century. He nds only weak evidence for long-run market power, but his data are at county rather than establishment level. However, studies of employer-size wage eects do not make much attempt to deal with the fact that, in the theory of imperfect competition in labor markets, both wages and employment are simultaneously determined by the employers choice of a prot-maximizing combination of employment and wage. Thus, one needs to nd another way of identifying the labor supply curve. Finding a suitable instrumental variable is the obvious approach and a few studies have taken this route.11 Sullivan (1989) tries to estimate the wage elasticity of the supply of nurses to individual hospitals using panel data. Essentially, he estimates an employer size wage eect for nurses, after controlling for other factors (for example, he includes individual hospital eects). As an instrument for the level of demand, he uses measures of the hospital caseload.12 With this approach, Sullivan estimates the wage elasticity of labor supply to be 1.26 in the short-run by estimating the relationship between changes in wages and changes in employment over a year. He estimates the wage elasticity of labor supply to be 3.86 in the longer run by estimating the relationship between changes in wages and changes in employment over several years. Are these elasticities large or not? Using the larger long-run elasticity and the formula in note 4, Sullivans estimates imply that wages will be 79 percent of marginal product. The implied gap between the wage and marginal product is not enormous, but is, for example, comparable in size to estimates of the union wage mark-up in the United States. More persuasive in its choice of instrument, in our view, is the recent study by Staiger et al. (1999). They investigate the impact on employment of an exogenous, legislated change in wages for registered nurses in hospitals run by the Veterans Administration (VA) in 1991. Prior to 1991, VA hospitals paid registered nurses based on a national scale; in 1991, the Nurse Pay Act (1990) required that VA hospitals set wages based on a survey of local hospitals. The basic model they estimate relates the change in employment at individual VA and non-VA hospitals to changes in wages relative to competitors and other relevant factors. They use a measure of the impact of the legislative change as an instrument for the relative wage. Their estimate of the short-run wage-elasticity of labor supply is quite low, around 0.1, and they conclude that hospitals have a signicant degree of wage-setting power in the market for nurses. Their approach seems a good one for several reasons. First, the change in wages can reasonably be thought of as exogenous. Second, initial wages in VA hospitals were low relative to the prevailing level of market wages for nurses.
couple of older studies on the subject of the elasticity in the labor supply curve facing an individual rm include Reynolds (1946) and Nelson (1972). 12 Sullivans caseload variables are in-patient days and length of stay. One might debate whether this is a good instrument but that is not our main purpose here. One problem is that caseloads are probably endogenous to the model, too. Indeed, the oligopsony model predicts that wages, employment and output are all endogenous and correlated in equilibrium. In this situation, the estimate of the elasticity of labor supply will most likely be biased upward.
For these reasons, this study seems to come closest to the ideal experiment one would like to conduct. But because it is dicult to nd examples of exogenous rm-specic wage changes, estimates of the wage elasticity facing an individual rm may remain few and far between. An alternative approach to measuring the market power of employers, used by Card and Krueger (1995) is to note that in a steady-state, the level of employment in a rm, denoted by N , can be written as the ow of recruits, R, divided by the separation rate, s, according to the formula N = R/s. For example, in each year, if a rm recruits 10 new employees and 10 percent of its existing employees quit, its steady state employment will be 100 employees. The elasticity of employment with respect to wages may then be decomposed as the elasticity of recruits with respect to wages minus the elasticity of separations with respect to wages. Estimates of the wage elasticity of separations have already been presented in Table 1: these and other estimates are rarely above one. Estimates of the wage elasticity of recruits are harder to nd but Card and Krueger (1995) survey a number of studies and conclude that 4 seems to be an upper bound. An upper bound for the overall wage elasticity is then 5, which, using the formula in note 4, predicts that wages are 17 percent below marginal productsa nding not far from that implied by Sullivans (1989) long-run estimate.
This paper has reviewed recent developments in labor economics that are based on the premise that employers have nonnegligible market power over their workers. The primary advantage of this approach is that it leads to a more natural view of the workings of labor markets and can readily explain apparently anomalous empirical ndings like the existence of wage dispersion, why employers pay for general training, why wages are related to employer characteristics and the impact of minimum wages on employment. Manning (2002) provides a more extensive review of the areas where oligopsony can help us to a better understanding of labor markets. The main sources of oligopsony power are likely to be preference heterogeneity over jobs, mobility costs, and imperfect information. We have chosen to motivate much of the paper using a particular model of preference heterogeneity using travel costs, though we could have used the other approaches as well. Direct evidence on the extent of oligopsony power is still rare (and deserves further future research) but the evidence we have suggests that it is not negligible. For some, the claim that employers have some oligopsony power has normative connotations about the ability of employers to exploit workers. We have tried to emphasize the positive aspects of oligopsony, without taking a normative position on whether this is good or bad. In fact, we think it is inevitable that employers have some oligopsony power, because the sources of that market power in labor markets are so universal.
Acemoglu, Daron and Jorn-Steen Pischke. 1999. Beyond Becker: Training in Imperfect Labor Markets, Economic Journal, vol. 109 pp. F112 142. Akerlof, George and Janet Yellen. 1985. A Near-Rational Model of the Business Cycle with Wage and Price Inertia, Quarterly Journal of Economics, supplement 100, 823838. Altonji, Joseph and Rebecca Blank. 1999. Race and Gender in the Labor Market, in Orley Ashenfelter and David Card (ed.) Handbook of Labor Economics, vol 3, Amsterdam: Elsevier Science. Becker, Gary. 1965. Human Capital: A Theoretical and Empirical Analysis, with Special Reference to Education, Chicago: University of Chicago Press. Becker, Gary. 1957. The Economics of Discrimination. Chicago: University of Chicago Press. Bhaskar, V. and Ted To. 1999. Minimum Wages for Ronald McDonald Monopsonies: A Theory of Monopsonistic Competition. Economic Journal. Vol. 109, pp. 190203. Bhaskar, V. and Ted To. 2001a. Reply: Minimum Wages for Ronald McDonald Monopsonies: A Theory of Monopsonistic Competition. Mimeo. Bhaskar, V. and Ted To. 2001b. Is Perfect Price Discrimination Really Ecient? An Analysis of Free Entry Equilibria. Working Paper. Bhaskar, V. and Ted To. 2001c. Oligopsony and Distribution of Wages. European Economic Review, forthcoming. Black, Dan. 1995. Discrimination in an Equilibrium Search Model, Journal of Labor Economics, Vol. 13, pp. 309334. Blanchower, David G., Andrew J. Oswald and Peter Sanfey. 1996. Wages, Prots and Rent-Sharing. Quarterly Journal of Economics, Vol. 111, pp. 227251. Blanchard, Olivier-Jean and Nobuhiro Kiyotaki. 1987. Monopolistic Competition and the Eects of Aggregate Demand. American Economic Review. Vol. 77, no. 4, pp. 64766. Boal, William M. 1995. Testing for Employer Monopsony in Turn-ofthe-Century Coal Mining. RAND Journal of Economics. Vol. 26, no. 3, pp. 51936. Boal, William M. and Michael R. Ransom. 1997. Monopsony in the Labor Market. Journal of Economic Literature. March, pp. 86112. Brander, James A. and Barbara J. Spencer. 1985. Export Subsidies and International Market Share Rivalry. Journal of International Economics. Vol. 18, no. 12, pp. 83100. Bunting, Robert L. 1962. Employer Concentration in local labor markets. Chapel Hill: University of North Carolina Press. Burdett, Kenneth and Dale Mortensen, 1998, Wage Dierentials, Employer Size, and Unemployment. International Economic Review. Vol. 39, no. 2, pp. 257273.21
Card, David and Alan B. Krueger. 1994. Minimum Wages and Employment: A Case Study of the Fast-Food Industry in New Jersey and Pennsylvania. American Economic Review. September, pp. 772793. Card, David and Alan B. Krueger. 1995. Myth and Measurement: The New Economics of the Minimum Wage. Princeton, NJ: Princeton University Press. Card, David and Alan B. Krueger. 2000. Minimum Wages and Employment: A Case Study of the Fast-Food Industry in New Jersey and Pennsylvania: Reply. American Economic Review. December, pp. 1397420. Dixit, Avinash and Joseph E. Stiglitz. 1977. Monopolistic Competition and Optimal Product Diversity. American Economic Review. Vol. 67, pp. 297308. Gibbons, Robert and Lawrence Katz. 1992 Does Unmeasured Ability Explain Inter-Industry Wage Dierentials? Review of Economic Studies July, pp. 515-536. Hotelling, Harold. 1929. Stability in Competition. Economic Journal, Vol. 39, pp. 4157. Idson, Todd L. and Walter Y. Oi. 1999. Workers Are More Productive in Large Firms. American Economic Review. Vol. 82, no. 2, pp. 104108. Keane, Michael P. 1993 Individual Heterogeneity and Inter-industry Wage Dierentials, Journal of Human Resources, vol. 28, pp. 134161. Krueger, Alan B. and Lawrence H. Summers. 1988 Eciency Wages and the Inter-Industry Wage Structure. Econometrica, Vol. 56, No. 2, Mar. 1988, pp. 259293. Krugman, Paul. 1979. Increasing Returns, Monopolistic Competition, and International Trade, Journal of International Economics, Vol. 9, 469479. Lester, Richard A. 1946 Wage Diversity and Its Theoretical Implications, The Review of Economic Statistics, Vol. 28, No. 3., pp. 152159. Mankiw, Gregory. 1985. Small Menu Costs and Large Business Cycles: A Macroeconomic Model of Monopoly, Quarterly Journal of Economics, Vol. 100, pp. 529539. Manning, Alan. 2002. Monopsony in Motion. London School of Economics. Murphy, Kevin and R. Topel. 1987. Unemployment, Risk, and Earnings: Testing for Equalizing Wage Dierences in the Labor Market, in Lang, K. and J. Leonard (Eds.) Unemployment and the Structure of Labor Markets. Basil Blackwell, London. Nelson, Philip. 1973. The Elasticity of Labor Supply to the Individual Firm. Econometrica, vol. 41, pp. 85366. Neumark, David and William Wascher. 2000. Minimum Wages and Employment: A Case Study of the Fast-Food Industry in New Jersey and Pennsylvania: Comment. American Economic Review. Vol. 90, no. 5, pp. 1362 1396. Pencavel, John H. 1972. Wages, Specic Training and Labor Turnover in U.S. Manufacturing Industries International Economic Review. vol. 13, pp. 5364. 16
Ransom, Michael R., William M. Boal and Paul M. Beck. 2000. Empirical Tests of Labor Monopsony: School Teachers in Missouri. Working paper. Reynolds, Lloyd. 1946. The Supply of Labor to the Firm. Quarterly Journal of Economics, vol. 60, pp. 390411. Reynolds, Lloyd G. 1951. The Structure of Labor Markets; Wages and Labor Mobility in Theory and Practice, Westport, Conn.: Greenwood Press. Salop, Steven C. Monopolistic Competition with Outside Goods. Bell Journal of Economics. Spring 1979, pp. 14156. Shapiro, Carl and Joseph E. Stiglitz, Equilibrium Unemployment as a worker Discipline Device. American Economic Review. Vol. 69, pp. 433444. Slichter, Sumner H. 1950. Notes on the Structure of Wages. The Review of Economics and Statistics, Vol. 32, No. 1, pp. 8091. Smith, Adam. 1776. An Inquiry into the Nature and Causes of the Wealth of Nations. Clarendon Press (1976): Oxford. Staiger, Douglas, Joanne Spetz and Ciaran Phibbs. 1999. Is There Monopsony in the Labor Market? Evidence From a Natural Experiment. NBER Working Paper #7258. Stevens, Margaret. 1994. A theoretical model of On-the-Job training with Imperfect Competition, Oxford Economic Papers, vol. 46, pp. 537562. Stigler, George. 1946. The Economics of Minimum Wage Legislation. American Economic Review, vol. 36, pp. 358365. Sullivan, Daniel. 1989. Monopsony Power in the Market for Nurses. Journal of Law and Economics. October, pp. S13578. Viscusi, W. Kip. 1980 Sex Dierences in Worker Quitting. Review of Economics and Statistics, vol. 62, pp. 38898. Walsh, Frank. 2001. Comment on: Minimum Wages for Ronald McDonald Monopsonies: A Theory of Monopsonistic Competition. Mimeo.
Table 1: Estimates of the Elasticity of Separations with Respect to the Wage PSID (US) NLSY (US) BHPS (UK) LFS (UK) mean separation rate 0.21 0.55 0.19 0.058 no controls 0.944 0.515 0.798 0.646 (0.030) (0.019) (0.032) (0.021) with controls 0.973 0.536 0.720 0.500 (0.041) (0.032) (0.041) (0.028) tenure controls 0.575 0.340 0.503 0.343 (0.037) (0.026) (0.064) (0.032) Notes. This Table reports the elasticities of separations with respect to the wage with standard errors in parentheses. The dependent variable is a zero-one dummy taking the value one if the individual left the job over the period (a year for all data sets except the LFS which uses a quarter). We model the instantaneous separation rate as s = ex so that the probability of still being in a job after a period of time is given by S = est . The elasticity of the quit rate with respect to the wage is then given by the coecient on the log wage. The row headed no controls simply includes the wage. The rows marked with control include education, race, marital status, children, region, a quartic in experience and year dummies. The row headed tenure control includes a quartic in tenure in addition to the usual controls. Standard errors are in parentheses.
Table 2: Low-Wage Workers Search for Other Jobs: UK Labor Force Survey dependent looking for looking for number of number of variable another job another job search methods search methods sample men women men Women log (wage) 0.032 0.014 0.464 0.273 (0.001) (0.001) (0.014) (0.021) number of obs 167390 173858 167398 173866 mean of dep 0.076 0.065 0.26 0.22 variable Notes. 1. The sample period is March 1993 to December 2000. The other controls included are race, education, experience, job tenure, month, year and region dummies. 2. When the dependent variable is looking for another job, a probit model is estimated. When the dependent variable is number of search methods, a poisson model is estimated: those who are not looking are assigned zero search methods. Standard errors are in parentheses.
Figure 1: Illustration of Worker Job Choice with Transportation Costs
w0 w0 net wage
x x location
Figure 2: Prot Maximization Under Oligopsony wage M C0 M C0
LS0 LS0
w0 w0
Figure 3: Illustration of Duopsony Equilibrium Using Employer Wage Reaction functions R1 R0 w0 R0 Firm 0s Wage w0
45 w1 Firm 1s Wage w1
Figure 4: Minimum Wages and Employment Under Oligopsony wage M Ci M Ci
LSi LSi
wm wi
Salario minimo
oligopolio
Fornitura (Economia)
Discriminazione dell'occupazione
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