I've recently seen several studies that look at correlates of religiousness and various social maladies in different population areas (e.g., countries, states).
The chart below, for example, looks at levels of religiousness an poverty, crime, divorce, and health. Lo and behold, the more religious states are the worst off on most these measures. A naive interpretation of these might hold that religion creates social maladies.
This brings us to the concept of an ecological fallacy. Basically, population-level correlations do not need to hold at the individual-level. From Wikipedia: "The term comes from a 1950 paper by William S. Robinson. For each of the 48 states in the US as of the 1930 census, he computed the literacy rate and the proportion of the population born outside the US. He showed that these two figures were associated with a positive correlation of 0.53 — in other words, the greater the proportion of immigrants in a state, the higher its average literacy. However, when individuals are considered, the correlation was −0.11 — immigrants were on average less literate than native citizens. Robinson showed that the positive correlation at the level of state populations was because immigrants tended to settle in states where the native population was more literate. He cautioned against deducing conclusions about individuals on the basis of population-level, or "ecological" data."
As such, the chart below does find correlations between religiousness and various maladies, but that is not necessarily evidence that a person who becomes religious than experiences more of these maladies. For example, the best available individual-level evidence shows us that:
There is certainly nothing wrong at looking at population-level correlations, we just need to realize what we can, and can not, learn from them.
Thank you Carson!