Immigration Costs Are Overstated, Study Finds PARIS - Public debate about immigration is being distorted by unfounded concerns over the financial burden that new arrivals put on governments, the Organization for Economic Cooperation and Development said in a report Thursday. Across the developed world, "the fiscal impact of immigration is close to zero," the organization said in the report, which compares the costs of immigration internationally. "The current impact of the cumulative waves of migration that arrived over the past 50 years is just not that large," it added, "whether on the positive or negative side." The O.E.C.D., which is based in Paris, noted that over the decade 2001-2011, immigration was responsible for 40 percent of the population growth in member countries. Nevertheless, that inflow was usually almost irrelevant to overall public expenditures relative to gross domestic product - "generally not exceeding 0.5 percent of G.D.P. in either positive or negative terms" - as the largest costs to government, like those from military spending, are unaffected by immigration. "Immigrants contribute more in tax and social contributions than they get in individual benefits," said Jean-Christophe Dumont, the O.E.C.D. official who headed the study. "That's why the net fiscal impact is mostly positive," even if small. "The public perception is that they take much more out than they put in," he said, "but that's just not the case." That message, however, has largely failed to sink in, the O.E.C.D. found, partly because some children of immigrants perform poorly in school and the job market and need government aid. In other cases, politicians find it easy to stereotype immigrants for political gain. While the study did not address the question of illegal immigration, Mr. Dumont said that "in most cases," such migrants are net contributors, since they pay many taxes but have limited access to public services like education and health. The O.E.C.D.'s findings were consistent with those of a recent Harvard Medical School study that found immigrants" contributions to Medicare in the United States had helped to create surpluses of $115 billion from 2002 to 2009 in the part of the program that pays for hospital care. That contrasted with a deficit of $28 billion for the American-born population over the same period. The O.E.C.D. compiled its report using statistical information provided by its member states for 2011, the most recent year for which the complete data were available, as well as some preliminary data for 2012. It noted that in some cases differences in definitions meant that the data were not always precisely compatible across countries. The organization's 34 members include most of the developed world nations, but exclude important emerging economies like China, Russia, India and Brazil. The organization enters the debate about immigration at a time when high unemployment and tepid economic growth, as well as questions about the viability of social welfare systems, have brought focus to the topic, with the discussion sometimes mixing economic issues and national identity in a politically potent brew. In Britain, the U.K. Independence Party has exploited unease with immigration, along with Britain's membership in the European Union, putting the dominant Conservative Party on guard. The Independence Party won about a quarter of the votes in local elections last month. In the United States, the Senate is considering a bill that would overhaul immigration laws, with the Republicans divided over a proposed path to citizenship for those residing in the country illegally and over questions of border security. The O.E.C.D. study found that the average age of immigrant populations affected their fiscal impact: The younger the immigrants, the greater the positive contribution. In a country like the United States, with a young immigrant base and relatively weak social welfare net, the positive impact is great, the study found. By contrast, in Germany, where the immigrant base is skewed toward people who arrived in the 1970s and are now retiring, the picture is more negative. Asia, largely China and India, was the source of 36 percent of all immigration to O.E.C.D. countries in 2011, the study found. China, with 10.3 percent of all immigration to O.E.C.D. nations, was the largest source, while India, at 4.7 percent, ranked fourth. Within Europe, Romania, at 6 percent, ranked second, while Poland, at 5.3 percent, ranked third.