Covariates
Generally, adjustments beyond age, calendar year and length of education rarely make substantial changes in risk estimates in epidemiological studies, including studies on risks and benefits of oral contraceptives. Nevertheless, a missing potential confounder is often claimed as invalidating a study if the message or results is disliked. An example is the missing control for family disposition of depression in study 1 and 2. That variable was included in study 3 and turned out not to be a confounder at all, indicating that when HC is prescribed, family history of psychiatric diseases is rarely taken into consideration.