Rekenen met ontbrekende gegevens

Conflict of interest: none declared. Financial support: none declared.

• In medical research missing data are sometimes inevitable.

• Different missingness mechanisms can be distinguished: (a) missing completely at random; (b) missing by design; (c) missing at random, and (d) missing not at random.

• If participants with missing data are excluded from statistical analyses, this can lead to biased study results and loss of statistical power.

• Imputation methods can be applied to estimate missing values; multiple imputation gives a good idea of the inaccuracy of the reconstructed measurements.

• The most common imputation methods assume that missing data are missing at random.

• Multiple imputation contributes greatly to the efficiency and reliability of estimates because maximum use is made of the data collected.

• Imputation is not meant to obviate low-quality data.