Average improvement indices

The WWC computes an average improvement index for each domain and each study and a domain average improvement index across studies of the same intervention (see the Technical Details of WWC-Conducted Computations).

The improvement index represents the difference between the percentile rank of the average student in the intervention condition and the percentile rank of the average student in the comparison condition. It can take on values between -50 and +50, with positive numbers denoting results favorable to the intervention group. Unlike the rating of effectiveness, which is based on four factors, the improvement index is based only on the size of the difference between the intervention and the comparison conditions. ¹

Staying in school

The staying in school domain includes measures of whether the student remained enrolled in school or dropped out of school without earning a high school diploma or GED certificate as well as the number of school days enrolled. The WWC reviewed outcomes in this domain for 9 dropout prevention programs, and the average improvement index ranged from -3 to +42 percentile points (figure 1).

Progressing in school

The progressing in school domain includes measures of credits earned, grade promotion, and whether the student is making normal progress toward graduation and the highest grade completed. The WWC reviewed outcomes in this domain for 11 programs, and the average improvement index ranged from -6 to +35 percentile points (figure 2).

Completing school

The completing school domain includes measures of whether the student earned a high school diploma or received a GED certificate. We reviewed outcomes in this domain for 11 programs, and the average improvement index ranged from -3 to +17 percentile points (figure 3).