Hypothetical true association
| True maternal BV (Nugent criteria) | Case-control status | |
|---|---|---|
| Cases (low birth weight) | Controls (normal birth weight) | |
| BV, bacterial vaginosis. “True” odds ratio = (60/140)/(40/160) = 1.71 (95% CI 1.06 to 2.79). | ||
| BV | 60 | 40 |
| No BV | 140 | 160 |
| Total | 200 | 200 |