Cochrane Handbook mentions subgroup analyses are only warranted if there are more than 10 studies (I have 28), and if they are distributed evenly among categories of subgroup. I am wondering if there is any guidance anywhere which is clearer. I.e. what is the uneven distribution ratio cut-off? I have 24 studies in one category and 4 in another, that feels too uneven for me to use, but I would like some rationale behind that please. Or another subgroup has multiple categories, with a split of studies like: 1,1,2,3,5,6,8 - is that ok, only having a single study in some categories?

Any other reference about these subgroup analysis decisions greatly appreciated.

Many thanks!

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