What is Simpson's paradox?

Simpson's paradox is a statistical phenomenon where a trend observed in several different groups of data reverses or disappears when these groups are combined.

Example: In product analytics, it might seem that a new feature worsens metrics for each user segment individually, but when all segments are combined, the feature actually improves overall metrics. This occurs due to differences in group sizes or other hidden factors.

Simpson's paradox highlights the importance of analyzing data at different levels and carefully choosing aggregation methods to avoid making erroneous conclusions.