Why a study attempting to replicate a nominally significant effect (p~0.05) which uses the same sample size as the original study has 50% of rejecting the null?

Question

Why a study attempting to replicate a nominally significant effect (p~0.05) which uses the same sample size as the original study has 50% of rejecting the null?

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Answer 1

this needs a little more explanation from you OP.

but from how I interpret what you’re asking is essentially “why is a follow-up study using essentially the same setup not nearly as confident to have found something?”

that might be that there was some other effect affecting the first study (basically an unidentified systematic error) or something like that.