However, some mental health professionals have opposed Beck's cognitive models and resulting therapies as too mechanistic or too limited in which parts of mental activity they will consider. From within the CBT community itself, one line of research using component analyses (dismantling studies) has found that the addition of cognitive strategies often fails to show superior efficacy over behavioral strategies alone, and that attempts to challenge thoughts can sometimes have a rebound effect. Moreover, although Beck's work was presented as a far more scientific and experimentally-based development than psychoanalysis (while being less reductive than behaviourism), Beck's key principles were not necessarily based on the general findings and models of cognitive psychology or neuroscience developing at that time but were derived from personal clinical observations and interpretations in his therapy office. And although there have been many cognitive models developed for different mental disorders and hundreds of outcome studies on the effectiveness of CBT—relatively easy because of the narrow, time-limited and manual-based nature of the treatment—there has been much less focus on experimentally proving the supposedly active mechanisms; in some cases the predicted causal relationships have not been found, such as between dysfunctional attitudes and outcomes.