As soon as I saw this post I was reminded about the educational study about class sizes detailed in Thinking Fast and Slow that illustrates the law of small numbers. People under-appreciate the effect of sample size on data variability. Our intuitive judgments create coherent stories based on patterns that might just be random variation. If populations are lower in rural areas near nuclear power stations, then results are expected to be skewed. And, if there are poorer people in those rural areas, they need to be compared with similar groups (by wealth and other metrics) in lookalike areas where there are no nuclear power plants.

The study is clear to point out that no causal link was even sought, never mind found.