Simpson’s paradox

What could we find worse than false information? What about perfectly accurate, scientifically sound information that suffers from Simpson’s paradox?

I confess that I only discovered this recently. Wikipedia describes Simpson’s paradox like this:

Simpson’s paradox, which also goes by several other names, 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 is unduly given causal interpretations. The paradox can be resolved when confounding variables and causal relations are appropriately addressed in the statistical modeling. Simpson’s paradox has been used to illustrate the kind of misleading results that the misuse of statistics can generate.

Apparently this has caused much of the confusions (sometimes accidental, sometimes not) around the efficacy of the various Covid-19 vaccines.

Flowing Data have an interesting article about this. Covid Actuaries have another valuable analysis.

Doctors recommend reading them one after the other.