Dear Mark I have another following question, how to interpret the result of EV3 in vertex analysis ? How to interpret the two meshes and vector direction in the result of EV3 ? By the way, whether the design matrix which illustrate below is correct for interaction analysis in shape analysis? EV1 EV2 EV3 -1 3 3 -1 1 1 -1 2 2 1 4 -4 1 5 -5 1 3 -3 PS: EV1 is group variable (-1: normal ; 1: patient) ; EV2 (raw data of behavior mesure) ; EV3 sorry to bother you ! Best KH