Gender e ffect Modification in the a ssociation Between s leep d eprivation and f alls
In their article on self reported sleep duration in communitydwelling older adults, Kuo and colleagues (1) concluded with an association of falls with shortened sleep duration in women but not in men. However, adjusted odds ratios of having suffered a fall in the previous year ranged from 1.35 to 2.79 in four different logistic regression models, with somewhat higher point estimates in equivalent analyses restricted to nonusers of psychotropic medications. These figures are more compatible with an effect than with absence of effect. The rationale for authors' conclusion was most probably a conventional interpretation of implicit hypothesis tests, the latter consisting of checking up whether the 95% confidence interval includes the null value. Apart from the dubiousness of such procedures (2) authors' analyses were not based on hypothesis testing but on point and interval estimation. A confidence interval includes a range of the parameter values more compatible with the data, beginning with the point estimate (2) Hence, data would be more compatible with the point estimate in the commented study an odds ratio of 2.79 than with any other value of the scale, including the null (odds ratio 1) Nonetheless, the majority of relevant models of the study seem to suffer from notable instability probably brought about by sample size scarcity, which can result in bias (3) Although affecting both sex strata, the impact of this problem on the males subsample was greater, not to mention on the likely power limitation of a potential test of homogeneity in that conditions. I believe a better conclusion should at least convey that the data did not permit an adequate measurement in men.