Changing predictors of statin initiation in US women over two decades.

Secular trends reflected evolution toward risk factor-based treatment indications for statin initiation with increased initiation among diabetics and women with normal and borderline cholesterol. The role of serum cholesterol changed over time, though the character was scale (multiplicative vs additive) dependent. In pharmacoepidemiologic studies of statins, strength of confounding by important variables sometimes unmeasured in claims data, such as cholesterol level, may be calendar time dependent.