multi-collinearity, tolerance, variance inflation factors, variance of regression coefficients,

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In the past decade, young people in the United States have been two to three times more likely than in the two previous decades to commit homicides, while those 25 years and older have been less likely to commit homicides than were members of their age groups in the earlier time period. These changes in youth homicide rates are associated with two cohort characteristics that are theoretically linked to criminality: relative size of cohorts and the percentage of cohort member born to unwed mothers. These effects persist throughout the life span, are independent of age and historical period, and can explain fluctuations in homicide arrest rates before the recent upturn.

Social scientists often use the mean of individual-level characteristics to describe aggregates such as organizations, schools, or programs. They seldom, however, attempt to assess the reliability of these measures. This article indicates how the internal consistency reliability of such measures can be estimated for several commonly used research designs. The method is based on generalizability theory and requires only the data that would normally be used to answer the substantive questions of a study; for example retests or parallel forms are not necessary.

No abstract