I do not want to run through the arguments for and against MYP, but I did look over the data about MYP and results in DP published by the IB and I think I can see the flaw in it. (Correct me if I am wrong.)

All the DP schools I have ever worked in (in Europe, Asia and Africa) get DP scores above the world average. These are also the schools that are most inclined to introduce MYP - that is International Schools around the globe. Not surprising most get better results now as most were getting better results anyway, being commited to the DP (and perhaps to the IB in general as much as to MYP in particular.)

Flip side somewhere in the world there must be a group of schools getting below average DP scores. The biggest proportion of DP schools in the world is still in U.S.A. Many of those are not international schools and I suspect are not really commited to the DP in the same way. The schools that I am talking about would not be offering MYP, which in any case does not fit at all well with the Middle School / High School system practised in U.S.

Hence the data is unlikely to be comparing like with like. It would take longer but be more valid to compare the same schools DP results before and after the introduction of MYP.

A slight advantage to CIS is that schools have to be CIS accredited to recruit through them. This is generally a sign of better quality schools. That does not mean to say that there are not some excellent schools at Search or not a few bad apples that have managed to get themselves CIS accredited but it might be something to bear in mind for beginners.