I wonder if this is due to allegiance effects [1] inflating the effect of CBT in the earlier studies. I would expect that the older a CBT study is, the more influence the originators and promoters of CBT had on it.<p>[1]: <a href="https:&#x2F;&#x2F;www.ncbi.nlm.nih.gov&#x2F;pubmed&#x2F;26033943" rel="nofollow">https:&#x2F;&#x2F;www.ncbi.nlm.nih.gov&#x2F;pubmed&#x2F;26033943</a>