To be a bit more specific, it's a meta-anslysis which is considered to be the top of the quality of scientific evidence pyramid. It has incorporated appropraite databases where the manuscripts were extracted from, and has followed specific guidelines for conducting a systematic review and meta-analysis.

There are of course limitations to this study, but every study has its limitations. It's also important to know the question that the mauscript is trying to answer, as the article will try not to diverge from this question.