# [Metrics Monday] Simpson’s Paradox, or Why “Determinants of…” Papers Are Problematic

From Wikipedia:

Simpson’s paradox, or the Yule-Simpson effect, is a paradox in probability and statistics, in which a trend appears in different groups of data but disappears or reverses when these groups are combined. … This result is often encountered in social-science and medical-science statistics, and is particularly confounding when frequency data is unduly given causal interpretations. The paradoxical elements disappear when causal relations are brought into consideration.

What does this mean, specifically? Suppose you are estimating the equation

(1)

with observational (i.e., nonexperimental) data, and you are interested in the causal effect of on . Suppose further that after estimating equation (1), you find that . Continue reading