Two basic data sources required for research studies have been secondary and primary. Secondary data collection helps the researcher to provide relevant background to the study and are, in most cases, available for retrieval from recorded sources. Primary data collection requires the researcher to venture into the field where the study is to take…

From a priori and post hoc data collection perspectives, this paper describes the interrelations among (1) power, alpha, effect size, and sample size for hypothesis testing; and (2) precision, confidence, and sample size for interval estimation. Implications for special education researchers working with convenient samples of fixed size are…