Reliabilität und Stabilität des Index der sozialen Benachteiligung und Kompositionseffekt der Schulen

School funding formulas have been much discussed to compensate the needs of socially disadvantaged schools. The index of social disadvantages (“Index der sozialen Benachteiligung”, ISB), a measure of the social and ethnical composition in Austrian schools, was suggested as a key variable for this purpose. It was reported in the context of the national standards-based assessment tests in 2013. The main topic of the presented article is to provide insights into the reliability and stability (over two consecutive measurement occasions) of the proposed index. Furthermore, we evaluated the school composition effect, indicating the relationship between school composition and performance. For all analyses data from the national standards-based assessment tests from 2012 and 2013 were used. The results – based on descriptive statistics and intraclass correlation coefficients – show that the school index is a sufficiently reliable measure. As expected however, the index proves to be less reliable for small schools than for schools with a higher number of students. In addition, as revealed by a multilevel analysis and conventional change measures, the index proofs to be stable over the two measurement occasions. Finally, the results of a multilevel latent covariate model show evidence for a composition effect, which holds for both primary and lower secondary schools. Also, the composition effect is evident even after controlling for school track.