Non-Independence of Nations: Revisiting a Centuries-Old Methodological Challenge

We revisit a critical problem of cross-cultural research: the non-independence of nations arising from shared ancestry and joint cultural diffusion. Recent review highlighted that few published cross-cultural studies attempt to control for such non-independence, often doing so inefficiently. This may compromise causal claims derived from such analyses. We reassess the problem and caution against using a one-size-fits-all “remedy” for non-independence. Non-independence can involve three distinct issues—(1) confounding by (un)observable variables, (2) Galton’s problem (joint diffusion and shared ancestry) as a special case of confounding, and (3) non-independence as a nuisance—each requiring a careful assessment of the causal model and a specific treatment. Controlling for non-independence by default may result in one of five outcomes, including successful elimination of the bias, improving precision, doing nothing, harming precision, or introducing bias, which we demonstrate with simulations. Instead of rolling a five-sided dice, we encourage cross-cultural scholars to begin with a careful evaluation of their underlying theoretical assumptions and causal models. In essence, we contribute to the refinement of cross-cultural research methodology by advocating for a tailored approach to addressing non-independence that models the real-world processes under examination.