Meta-analysis of 23 between-group direct observation studies of children with ADHD and typically developing peers indicates significant deficiencies in children with ADHD's ability to pay attention in classroom settings. Comparison with 59 single case design studies of children with ADHD suggests generalizability of between-group comparisons. Weighted regression analysis determined that several methodological differences – sample characteristics, diagnostic procedures, and observational coding schema – have significant effects on observed levels of attentive behavior in the classroom. Best case estimation indicates that after accounting for these factors, children with ADHD are on-task approximately 65% of the time compared to 85% for their classroom peers. Children with ADHD were also more variable in their attentive behavior across studies. Implications for conceptual models of ADHD are discussed.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

Meta-analysis has been widely used in clinical research because it provides a useful tool for combining results from a series of trials addressing the same question. Two major approaches for study-to-study variation can be used in a meta-analysis: the fixed effects model which assumes that each study has the same true effect size, and the random effects model which assumes that the true effect size is a random variable that varies between studies. When there are covariates arising from the study, regression models can be used to explain the effects of these covariates on the between study variation in effect size. The purpose of this project is to draw some general conclusions about the statistical methods used in meta-analyses by re-examining several clinical examples which presented some problems. Four illustrative examples of recent meta-analyses were selected and re-examined. Both fixed effects and random effects models were used. In addition, regression models were used in two examples. Some general conclusions were made about the statistical aspects of meta-analysis from this project. The overall estimate of the fixed effects model tends to be overly influenced by large trials and may results in contradictory conclusions when extreme trials (small vs. large samples) are combined. Therefore, it is advocated that the weights allocated to each trial in any meta-analysis should be explicitly calculated and displayed. The random effects model takes a more balanced account of all studies and considers other unknown factors which may affect the effect size. Therefore, the random effects model and random effects regression model are more appropriate for these clinical data meta-analyses. / Thesis / Master of Science (MS)