Instrumentele-variabele-analyse

Conflict of interest: none declared. Financial support: financial support for this article was received from the Netherlands Organisation for Health Research and Development (ZonMw; grant no. 152002040).

• Instrumental variable analysis is a recently propagated method to deal with confounding and to estimate therapeutic effects in observational studies.

• An instrumental variable is a factor which affects treatment but is not related to patient prognosis.

• A theoretical advantage of a well-chosen instrumental variable is that both measured and unmeasured confounders do not influence the effect estimator.

• Examples of instrumental variables previously used are regional differences in treatment and physician prescribing preference.

• Application of instrumental variable analysis seems most suited to large patient registries with considerable expected residual confounding in case standard analytical methods are applied.