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Improvement index
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 Technical Details of WWC-Conducted Computations). 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 based entirely on the size of the effect, regardless of the statistical significance of the effect, the study design, or the analyses. The improvement index can take on values between -50 and +50, with positive numbers denoting results favorable to the intervention group.
The average improvement index for progressing in school is +7 percentile points based on the one study that passed WWC evidence screens, with a range of +6 to +8 percentile points across the findings.
Summary
The WWC reviewed four studies on Talent Development High Schools. One study met WWC standards with reservations; the remaining studies did not meet WWC evidence screens. Based on this one study, the WWC found potentially positive effects on progressing in school. The conclusions presented in this report may change as new research emerges.