Misuse of ANOVA with cumulative intakes.

Cumulative responses are important for the study of ingestive behavior. The total amounts consumed at several time points after experimental or control treatments are often analyzed using a mixed-model analysis of variance. The method used by some investigators to calculate the significance of this difference is invalid and may lead to serious errors of inference. Direct analysis of cumulative data can lead to grossly erroneous p-values for certain effects because data from early time points contribute disproportionately to the outcome. Analysis of uncumulated data yields the appropriate levels of significance and all of the same hypotheses can be tested.