period.¹ Nor are there longitudinal studies that provide trend data for population cohorts or that track the progression of individuals into or out of the states of pathological or problem gambling. Finally, literature on pathological and problem gambling rarely distinguishes, in an epidemiological sense, the difference between rates of pathological and problem gambling and proportions of pathological and problem gamblers. This distinction is made throughout the chapter to the extent allowed by the data available to the committee.

Perhaps the most serious limitation of existing prevalence research is that the volume and scope of studies are not sufficient to provide solid estimates for the national and regional prevalence of pathological and problem gamblers, or to provide estimates of changes in prevalence associated with expanded gambling opportunities and other recent secular trends. Only three studies have attempted to measure the prevalence of pathological or problem gambling in the United States for more than one or a few states. A national study was undertaken by the University of Michigan Survey Research Center in 1975 (Commission on the Review of the National Policy Toward Gambling, 1976; Kallick et al., 1979). At that time, illegal gambling was believed to be widespread, and the nation was facing the prospect of increased legalization of gambling. Accordingly, the survey concentrated on assessing American gambling practices and attitudes toward gambling. The scale that attempted to measure "compulsive gambling" was only one small component of the larger gambling survey (Commission on the Review of the National Policy Toward Gambling, 1976).

From the responses of 1,736 adults about behaviors over their lifetimes, "it was estimated that 0.77 percent of the national sample could be classified as 'probable' compulsive gamblers,