The Globe reports about and posts a PDF of a letter from Massachusetts' Attorney General Office (AGO) back to Partners Healthcare System (see my earlier post on their assessment). And they don't give back an inch!
The AGO claim that the Dreyer report for Partners confirms their findings, in particular that quality is not related to variation in charges. They also call their methods (bivariate models) "extensively vetted and corroborated" and "anything other than sound" and found "flaws and errors in [Dreyer's] methodology.
I still think that Dreyer's multivariate approach is better although he does not apply it to the real interesting question: quality and how it relates to charges. I think they should all dig deeper and neither of their report is at all acceptable.