Averaging per-day conversion rates instead of pooling can flip your result — Simpson's paradox in a funnel.

Averaging per-day conversion rates instead of pooling can flip your result — Simpson's paradox in a funnel.
The error: weekday traffic converts at 4%, weekend at 1%, mix shifts between variants, and the daily-averaged "rate" lies about the pooled truth.
— Cause: unequal traffic composition across the comparison window.
— Fix: compute conversions/sessions pooled over the whole period, and check the variant traffic split matches by segment.
Read the number, not the story. [Simpson's paradox · pooled vs averaged]