I have another question on the OP’s premise: even toddlers etc. have to choose. Is there some magic that lets them rationalize the right button? Or is it a case of “oooooooh pwetty wed button” and BANG BANG BANG on the button?
I know I for sure directly answered your question (15-20% if i recall, although I now think that’s too high. I’d say about 3-5% now), and I think several others too.