<p>This study evaluates the validity of the epidemiological approach, which uses migrant samples to isolate cultural transmission effects from confounding factors. A key assumption of this approach is that emigrants accurately reflect the cultural values of their ancestral country. However, if migration is selective, using attitudes from the population of the ancestral country as a proxy for emigrant values may introduce measurement error. We test this assumption by comparing the cultural values of emigrants to the ancestral-country population, focusing on cooperation and religiosity. To better capture potential misrepresentation, we introduce a birth-cohort-based measure that links emigrant values to their ancestral-country counterparts over time. Our results indicate that while cooperation values are comparable, ancestral-country measures significantly underestimate religious values. These findings imply that the epidemiological approach remains valid, yet caution is warranted when systematic measurement errors are likely to bias the estimated cultural effects, particularly for traits that influence or are influenced by migration decisions.</p>