Technical Manual - Renaissance Learning

ValiditySTAR Early Literacy Enterprise Research Study ProceduresFigure 11 displays the scatterplot of the service version Rasch ability scores versusthe Enterprise scores. The plot illustrates the strong linear relationship betweenscores on the two tests.Figure 11: Plot of STAR Early Literacy Average “Service” Rasch Scores versus STAREarly Literacy Enterprise Rasch ScoresThe magnitudes of these correlation coefficients are attenuated by theunreliability in both tests. Correcting the Rasch and scaled score correlations forattenuation, using the formula developed by Spearman (1904), results incorrected correlations shown in Table 38.Table 38:Correlations between Enterprise and Service Version Scaled Scores andRasch Scores, Corrected for AttenuationAverage ServiceScaled ScoreAverage ServiceRasch ScoreEnterprise Scaled Score 0.91Enterprise Rasch Score 0.93The corrected correlations shown in Table 38 are high, but substantially less than1.00. This implies that the Enterprise and service versions are measuring highlyrelated, but not identical, constructs.To make scores on the Enterprise version comparable to STAR Early Literacyservice version scores, a scale linkage was performed, using a linear equatingapproach. The resulting linkage equation is:Equivalent STAR Early Literacy Service Rasch Ability Score =0.9746 × Enterprise Rasch Score – 0.1350STAR Early LiteracyTechnical Manual90