Sample Ratio Mismatch and Survivorship Bias: A Post-Mortem on a GIF-Removal Experiment

The experiment itself closed quietly, with no significant difference at the full-population level. What's worth writing up isn't the headline result — it's a secondary subgroup cut of the same data that looked like a clear win, and turned out to be a textbook case of sample ratio mismatch manufacturing a guardrail lift out of nothing...

The Experiment

A category browse page shows product cards, some with an animated GIF preview instead of a static thumbnail...

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