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Why summing your experiment wins overstates impact

Blog post from GrowthBook

Post Details
Company
Date Published
Author
Hampus Poppius
Word Count
2,172
Company Posts That Month
25
Language
English
Hacker News Points
-
Post removed?
No
Summary

The text discusses the concept of the "winner's curse" in the context of experimental results, highlighting how summing significant results from multiple experiments can lead to an overestimation of their true impact. This bias arises because experiments that pass the significance threshold often do so due to favorable random noise, causing inflated estimates. The text uses examples, such as Airbnb's findings, to illustrate how much the reported impact can differ from reality. To address this, it suggests using a "holdout" group—a subset of users not exposed to new changes—to get a more accurate measure of impact, as well as considering replication and Bayesian adjustments to correct for bias. The piece emphasizes the importance of understanding the mechanics of hypothesis testing and the limitations of aggregating results based solely on significance, warning against over-reliance on these inflated figures for decision-making.

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