title: Missing data approaches in eHealth research: simulation study and a tutorial for nonmathematically inclined researchers.
abstract: BACKGROUND
  Missing data is a common nuisance in eHealth research: it is hard to prevent and may invalidate research findings.
  
  
  OBJECTIVE
  In this paper several statistical approaches to data "missingness" are discussed and tested in a simulation study. Basic approaches (complete case analysis, mean imputation, and last observation carried forward) and advanced methods (expectation maximization, regression imputation, and multiple imputation) are included in this analysis, and strengths and weaknesses are discussed.
  
  
  METHODS
  The dataset used for the simulation was obtained from a prospective cohort study following participants in an online self-help program for problem drinkers. It contained 124 nonnormally distributed endpoints, that is, daily alcohol consumption counts of the study respondents. Missingness at random (MAR) was induced in a selected variable for 50% of the cases. Validity, reliability, and coverage of the estimates obtained using the different imputation methods were calculated by performing a bootstrapping simulation study.
  
  
  RESULTS
  In the performed simulation study, the use of multiple imputation techniques led to accurate results. Differences were found between the 4 tested multiple imputation programs: NORM, MICE, Amelia II, and SPSS MI. Among the tested approaches, Amelia II outperformed the others, led to the smallest deviation from the reference value (Cohen's d = 0.06), and had the largest coverage percentage of the reference confidence interval (96%).
  
  
  CONCLUSIONS
  The use of multiple imputation improves the validity of the results when analyzing datasets with missing observations. Some of the often-used approaches (LOCF, complete cases analysis) did not perform well, and, hence, we recommend not using these. Accumulating support for the analysis of multiple imputed datasets is seen in more recent versions of some of the widely used statistical software programs making the use of multiple imputation more readily available to less mathematically inclined researchers.
authors.affiliation: Arkin Academy, Amsterdam, The Netherlands. m.blankers@amc.uva.nl
authors.forename: Matthijs
authors.initials: M
authors.lastname: Blankers
authors.forename: Maarten W J
authors.initials: MW
authors.lastname: Koeter
authors.forename: Gerard M
authors.initials: GM
authors.lastname: Schippers
mesh_terms: D000328:Adult; D000428:Alcohol Drinking / Q000628:therapy*; D000465:Algorithms; D015331:Cohort Studies; D003627:Data Interpretation, Statistical; D001330:Electronic Data Processing / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D016247:Information Storage and Retrieval / Q000706:statistics & numerical data*; D008297:Male; D008490:Medical Informatics; D016347:Medical Records Systems, Computerized / Q000706:statistics & numerical data*; D008875:Middle Aged; D015233:Models, Statistical; D009426:Netherlands; D011446:Prospective Studies; D012107:Research Design; D015983:Selection Bias; D013813:Therapy, Computer-Assisted / Q000706:statistics & numerical data*; D055815:Young Adult