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The odds ratio is the cross-product ad/bc. It is the natural measure for case-control studies, where incidence cannot be estimated directly, and its confidence interval is computed on the log scale.
Odds ratio
OR = ad / bc
Confidence interval
exp(ln OR ± 1.96·√(1/a + 1/b + 1/c + 1/d))
OR = 1800/300 = 6, with a 95% interval of roughly 2.72 to 13.24 — clearly above 1.
When the outcome is rare, under about 10%; for common outcomes the odds ratio exaggerates the risk ratio.