Simpson’s paradox

Source: 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. It is sometimes given the impersonal title reversal paradox or amalgamation paradox. 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. Many statisticians believe that the mainstream public should be informed of the…