Its development co-occurred with that of relational frame theory, with several researchers such as Steven C Hayes being involved with both. ACT has been argued to be based on relational frame theory,[2] although this is a matter of some debate within the community.[3] Originally this approach was referred to as comprehensive distancing.[4] Every practitioner mixes acceptance with a commitment to one's values. These ingredients become enmeshed into the treatment in different ways which leads to ACT being either more on the mindfulness side or more on the behavior-changing side.[5] ACT has, as of September 2015, been evaluated in over 130 randomized clinical trials for a variety of client problems.[6] Overall, when compared to other active treatments designed or known to be helpful, the effect size for ACT is a Cohen's d of around 0.6,[7][8] which is considered a medium effect size.