research methods
statistics and research methods
epidemiological concepts
methods
Natural experiments are designs that occur in nature and permit a test of an otherwise untestable hypothesis and thereby provide leverage to disentangle variables or processes that would otherwise be inherently confounded. Experiments in nature do not, by definition, have the sort of leverage that traditional experiments have because they were not manufactured to precise methodological detail; they are fortuitous. [Source: Encyclopedia of Research Design; Natural Experiments]
natural experiments