An appropriate estimate of statistical power is critical for the design of intervention studies. Although the inclusion of a pretest covariate in the test of the primary outcome can increase statistical power, samples selected on the basis of pretest performance may demonstrate range restriction on the selection measure and other correlated…

This study examined the effectiveness of a researcher-provided intervention with fourth graders with significant reading difficulties. The intervention emphasized multisyllable word reading, fluent reading of high-frequency words and phrases, vocabulary, and comprehension. To identify the participants, 1,695 fourth-grade students were screened…