I'm running a AB testing at my company, but the split is somehow different than 50-50.

Is my test still correct? Can the split be 55-45, or 60-40, and so on?

When should I be worried?

Sorry if the question is too vague, but I believe it's very straightforward and I haven't seen any similar question.


There is hardly any problem at performing a A/B test whith unequal sample sizes. But you don't want samples too unbalanced because the precision of the test depends more on the lesser sample size than on the greater (the biggest they are, the better, I bet you already know).

Therefore, an A/B test with sample sizes 50 and 50 is more powerful than the same test with sample sizes 20 and 80.

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