Abstract
A recent study by Abt Associates (Abt/Carlson) purported to show that increments to prison capacity would lead to growth in prison population to fill that added capacity two years later. That finding has rapidly attained broad circulation and widespread acceptance. The original conclusion was based on a coefficient of 1.02 in a simple regression equation that represents change in prison population as a function of lagged changes in prison population and capacity. Reanalysis of the data shows that the original estimates resulted from a computation error; when that error is corrected the coefficient estimate is reduced to .264. Furthermore, two data points were particularly influential in the regression analysis, and omitting them results in a coefficient of .095 which is not statistic ally significant. Thus, the coefficient on which the original conclusion was based is eliminated in importance.
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