“…Since the first introduction of the term in 2000, the scientific community has adopted this concept in planning and conducting empirical studies. The researcher acknowledge that many authors explicitly refer back to the foundational papers published on the topic to justify experimental designs, to provide rationale for goals or structure of their evaluation studies (Ortigosa and Carro, 2003;Gena, 2005;Goren-Bar et al, 2005;Petrelli and Not, 2005;Arruabarrena et al, 2006;Glahn et al, 2007;Kobsa, 2007;Nguyen and Santos Jr, 2007;Ley et al, 2009;Limongelli et al, 2008;Popescu, 2009;Santos and Boticario, 2009) or to demonstrate methodological shortcomings of existing studies (Masthoff, 2002;Gena, 2005;Brusilovsky et al, 2006;Yang and Huo, 2008;Brown et al, 2009). The fact that layered evaluation received such a high level of attention in the literature reaffirms the claim that the evaluation of adaptive systems implicates some inherent difficulties.…”