[frostpine]

I think there are a lot of limitations with this article.

Its hard to track your mesh search terms, but looks like you are searching for improvement AND a lot of other search terms. Aren't you filtering out any articles which show deterioration?

I think a meta analysis is probably what you are actually looking for. It would be better, I think, to read some of these and manually include relevant references.

Neither of your assumptions are true.