Unambiguously, adaptive systems have to be evaluated empirically to guarantee that the adaptivity really works. Nevertheless, only few of the existing adaptive systems have been evaluated. One of the most important reasons for this lack is, that measures for adaptivity success have not been investigated systematically up to now. The aim of this PhD thesis is to explore a methodology for the empirical evaluation of adaptive systems, including validated criteria, experimental designs and procedures. It will be demonstrated that cognitive and behavioral factors provide important evidence for adaptivity success.