Dodo bird supporting researchers have found anti-Dodo bird supporters' research to also be "agenda"-based. For example, Wampold (2009) found Siev et al.'s (2007) study whose research for significance of CBT (Cognitive Behavior Therapy) versus RT (Rational Therapy) was resting on one experiment with an uncharacteristically large effect size (1.02) by Clark et al. (1994). Wampold found this effect size to be invalid because of the internal biases of the study. When this flawed experiment was removed from the analysis, the effect size was not statistically significant for the use of CBT over RT in panic disorder therapy. Against this research, in support of the anti-Dodo bird verdict, Chambless (2002) stated that "errors in data analysis, exclusion of research on many types of clients, faulty generalization to comparisons between therapies that have never been made, and erroneous sorts of treatments for all sorts of problems can be assumed to represent the difference between any two types of treatment for a given problem."