Most study samples show less variability in key variables than do their source populations due most often to indirect selection into study participation associated with a wide range of personal and circumstantial characteristics. Formulas exist to correct the distortions of population-level correlations created. Formula accuracy has been tested…

Objective and methods: To explore association between prevalence of ADHD and levels of risk for gestational alcohol exposure, the authors reviewed the charts of 2,231 youth referred for fetal alcohol spectrum disorders. Participants were categorized into four groups by different levels of risk for gestational alcohol exposure. For each group, the…