CV and mad panic behaviour

[LP]

For those interested a meta-analysis is a statistical analysis of multiple previous studies, there is a nice description of Wikipedia.
https://en.wikipedia.org/wiki/Meta-analysis

While meta-analysis can be useful, the big problem is they are easily distorted by selection methods, what studies/data to include and what studies/data to reject. It's most useful when all studies are included, but this can even become problematic when bogus studies/data become numerically dominant. At that time a meta-analysis becomes worthless and must be supplanted by a large study.

Adding any quantity of small studies together no matter how many does not supersede the results of a single large study, because all small studies are likely to contain the same bias. As Wikipedia puts in quite nicely;

A meta-analysis of several small studies does not always predict the results of a single large study. Some have argued that a weakness of the method is that sources of bias are not controlled by the method: a good meta-analysis cannot correct for poor design or bias in the original studies. This would mean that only methodologically sound studies should be included in a meta-analysis, a practice called 'best evidence synthesis'.

This is a big reason why the hacks are always posting/quoting you results of a meta-analysis, often nested as a meta-analysis of a meta-analysis of a meta-analysis.