title: Missing value imputation in longitudinal measures of alcohol consumption.
abstract: Attrition in longitudinal studies can lead to biased results. The study is motivated by the unexpected observation that alcohol consumption decreased despite increased availability, which may be due to sample attrition of heavy drinkers. Several imputation methods have been proposed, but rarely compared in longitudinal studies of alcohol consumption. The imputation of consumption level measurements is computationally particularly challenging due to alcohol consumption being a semi‐continuous variable (dichotomous drinking status and continuous volume among drinkers), and the non‐normality of data in the continuous part. Data come from a longitudinal study in Denmark with four waves (2003–2006) and 1771 individuals at baseline. Five techniques for missing data are compared: Last value carried forward (LVCF) was used as a single, and Hotdeck, Heckman modelling, multivariate imputation by chained equations (MICE), and a Bayesian approach as multiple imputation methods. Predictive mean matching was used to account for non‐normality, where instead of imputing regression estimates, "real" observed values from similar cases are imputed. Methods were also compared by means of a simulated dataset. The simulation showed that the Bayesian approach yielded the most unbiased estimates for imputation. The finding of no increase in consumption levels despite a higher availability remained unaltered.
authors.affiliation: Institute for Biometrics and Clinical Epidemiology, Charité – University Medicine Berlin, Germany. ulrike.grittner@charite.de
authors.forename: Ulrike
authors.initials: U
authors.lastname: Grittner
authors.forename: Gerhard
authors.initials: G
authors.lastname: Gmel
authors.forename: Samuli
authors.initials: S
authors.lastname: Ripatti
authors.forename: Kim
authors.initials: K
authors.lastname: Bloomfield
authors.forename: Matthias
authors.initials: M
authors.lastname: Wicki
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000428:Alcohol Drinking / Q000453:epidemiology*; D003198:Computer Simulation; D003625:Data Collection / Q000379:methods* / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D008953:Models, Anatomic; D011237:Predictive Value of Tests; D013997:Time Factors; D055815:Young Adult