If you are looking at ways to improve the meta-analysis methodology and adress the existing gaps and shortcomings of meta-analysis, it can in itself be a thesis topic contributing to the improvement of research methods in scientific inquiry.

Definitely no. Since Meta is just a type of review，not original research，cannot meet the innovatiion demands of PhD degree.

Hello, yes of course, because even when you are using this methodological strategy, you can also pose a research hypothesis. Here the data collection comes from individual studies related to your hypothesis. The important thing in meta-analysis is to define your research question through various strategies,for example through the “PICO” approach. Regards.

A similar question was asked earlier and the answers to that question can be useful.

Link to the question: https://www.researchgate.net/post/Is-Cochrane-systematic-review-as-a-PhD-thesis-possible-in-India

How might a systematic review fit within doctoral work?

The following benefits and limitations of utilizing systematic reviews for PhD dissertation work have been identified by students and faculty (Clark, personal communication, 23 November 2014; Daigneault, Jacob, & Ouimet, 2012; Minnie, van der Walt, , Klopper, & Cummings, 2010; Perry & Hammond, 2002; Sambunjak & Puljak, 2010).

Few more examples of PhD theses and dissertations in systematic review and meta-analysis available at: http://nordic.cochrane.org/research-highlights

https://www.uvic.ca/hsd/nursing/assets/docs/graduate/policies/systematic-review.pdf

http://nordic.cochrane.org/research-highlights

https://www.ncbi.nlm.nih.gov/pubmed/11372012