Simpson's paradox
Sign in to saveAlso known as Simpson paradox, reversal paradox, amalgamation paradox, Yule–Simpson effect, Simpson's reversal
phenomenon in probability and statistics, in which a trend appears in several different groups of data but disappears or reverses when these groups are combined
~15 min read
Encyclopedic overview
Simpson's paradox for quantitative data: a positive trend ( , ) appears for two separate groups, whereas a negative trend ( ) appears when the groups are combined. Visualization of Simpson's paradox on data resembling real-world variability indicates that risk of misjudgment of true causal relationship can be hard to spot.
Simpson's paradox is a phenomenon in probability and statistics in which a trend appears in several groups of data but disappears or reverses when the groups are combined. This result is often encountered in social-science and medical-science statistics, and is particularly problematic when frequency data are unduly given causal interpretations. The paradox can be resolved when confounding variables and causal relations are appropriately addressed in the statistical modeling (e.g., through cluster analysis).
Excerpted from Wikipedia’s “Simpson's paradox” article, available under the CC BY-SA 4.0 licence.