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The WWC computes an improvement index for each individual finding. In addition, within each outcome domain, the WWC computes an average improvement index for each study and an average improvement index across studies (see WWC Procedures and Standards Handbook, Appendix F). The improvement index represents the difference between the percentile rank of the average student in the intervention condition versus the percentile rank of the average student in the comparison condition. Unlike the rating of effectiveness, the improvement index is entirely based on the size of the effect, regardless of the statistical significance of the effect, the study design, or the analysis. The improvement index can take on values between –50 and +50, with positive numbers denoting favorable results for the intervention group.
Based on two studies, the average improvement index for Let’s Begin with the Letter People® on four measures of oral language is +1 percentile point with a range of –1 to +3 percentile points across findings. The average improvement index for nine measures of print knowledge is +6 percentile points across the two studies, with a range of +1 to +12 percentile points across findings. Based on one study, the average improvement index for Let’s Begin with the Letter People® on one measure of phonological processing is –5 percentile points, and the average improvement index on three measures of math is +3 percentile points, with a range of –4 to +8 percentile points.
The WWC reviewed five studies of Let’s Begin with the Letter People®. Two of these studies meet WWC evidence standards. Three studies do not meet either WWC evidence standards or eligibility screens. Based on the two studies, the WWC found no discernible effects of Let’s Begin with the Letter People® on oral language, print knowledge, phonological processing, and math. The conclusions presented in this report may change as new research emerges.
|Institute of Education Sciences
Early Childhood Education