When collating the papers, nobody is blinded to anything so it’s very, very easy to remove papers that the people doing the analysis disagree with...
A good systematic review (meta-analysis is the quantitative component thereof, although the terms are often incorrectly used interchangeably) will define inclusion criteria before beginning the review. Papers are then screened independently by multiple parties to see if they fit these criteria, in attempt to limit introducing bias in the choice of which to include. It shouldn’t be quite as arbitrary as you imply.
On top of this, many of them include additional unpublished (and therefore unreviewed) data from trials included in the analysis.
This is meant to counter publication bias, although it’s fraught with difficulties. Your comment seems to imply that this practice deliberately introduces bias, which is not necessarily the case.
Are you aware of the PRISMA statement? If so, can you suggest improvements to the recommended reporting of systematic reviews?
A good systematic review (meta-analysis is the quantitative component thereof, although the terms are often incorrectly used interchangeably) will define inclusion criteria before beginning the review. Papers are then screened independently by multiple parties to see if they fit these criteria, in attempt to limit introducing bias in the choice of which to include. It shouldn’t be quite as arbitrary as you imply.
This is meant to counter publication bias, although it’s fraught with difficulties. Your comment seems to imply that this practice deliberately introduces bias, which is not necessarily the case.
Are you aware of the PRISMA statement? If so, can you suggest improvements to the recommended reporting of systematic reviews?