Neuropsychometric tests in cross sectional and longitudinal studies - A regression analysis of ADAS - Cog, SKT and MMSE

Introduction: In clinical and drug studies; different neuropsychometric tes ts are used. So far, no empirical data have been published to compare studi es using different tests. The purpose of this study was to calculate a regr ession formula allowing a comparison of cross-sectional and longitudinal da ta from three neuropsychometric tests that are frequently used in drug stud ies (Alzheimer's Disease Assessment Scale, ADAS-cog; Syndrom Kurz Test, SKT ; Mini Mental State Examination, MMSE). Method: 177 patients with dementia according to ICD10 criteria were studied for the cross sectional and 61 for the longitudinal analysis. Correlations and linear regressions were calcul ated between tests. Significance was proven with ANOVA and t-tests using th e SPSS statistical package. Results: Significant Spearman correlations and slopes in the regression occurred in the cross sectional analysis (ADAS-cog -SKT r(s) = 0.77, slope = 0.45, SKT-ADAS-cog slope = 1.3, r(2) = 0.59; ADAS -cog-MMSE r(2) = 0.76, slope = 0.42, MMSE-ADAS-cog slope = -1.5, r(2)=0.64; MMSE-SKT r(s) = -0.79, stope = -0.87, SKT-MMSE slope = -0,71, r(2) = 0.62; p < 0.001 after Bonferroni correction; N-177) and in the longitudinal anal ysis (SKT-ADAS-cog, r(s) = 0.48, slope = 0.69, ADAS-cog-SKT slope = 0.69, p < 0.001, r(2) = 0.32, MMSE-SKT, r(s) = 0.44, slope = -0.41, SKT-MMSE, slop e = -0.55, p < 0.001, r(2) = 0.21). Conclusions: The results allow calculat ion of ADAS-scores when SKT scores are given, and vice verse. In longitudin al studies or in the course of the disease, scores assessed with the ADAS-c og and the SKT may now be statistically compared. In all comparisons, botto m and ceiling effects of the tests have to be taken into account.