Multiple imputation strategies for zero-inflated cost data in economic evaluations: which method works best?
Cost and effect data often have missing data because economic evaluations are frequently added onto clinical studies where cost data are rarely the primary outcome. The objective of this article was to investigate which multiple imputation strategy is most appropriate to use for missing cost-effectiveness data in a randomized controlled trial. Three incomplete data sets were generated from a complete reference data set with 17, 35 and 50 % missing data in effects and costs. The strategies evaluated included complete case analysis (CCA), multiple imputation with predictive mean matching (MI-PMM), MI-PMM on log-transformed costs (log MI-PMM), and a two-step MI. Mean cost and effect estimates, standard errors and incremental net benefits were compared with the results of the analyses on the complete reference data set. The CCA, MI-PMM, and the two-step MI strategy diverged from the results for the reference data set when the amount of missing data increased. In contrast, the estimates of the Log MI-PMM strategy remained stable irrespective of the amount of missing data. MI provided better estimates than CCA in all scenarios. With low amounts of missing data the MI strategies appeared equivalent but we recommend using the log MI-PMM with missing data greater than 35 %.
Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands. j.l.macneil-vroomen@amc.uva.nl.
Janet
J
MacNeil Vroomen
Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
Iris
I
Eekhout
Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
Marcel G
MG
Dijkgraaf
Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
Hein
H
van Hout
Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
Sophia E
SE
de Rooij
Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
Martijn W
MW
Heymans
Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
Judith E
JE
Bosmans
D000328:Adult; D003362:Cost-Benefit Analysis / Q000379:methods*; D003627:Data Interpretation, Statistical; D005260:Female; D006556:Heroin Dependence / Q000188:drug therapy / Q000191:economics; D006801:Humans; D016015:Logistic Models; D008297:Male; D008691:Methadone / Q000191:economics / Q000627:therapeutic use; D008875:Middle Aged; D019057:Quality-Adjusted Life Years; D016032:Randomized Controlled Trials as Topic
D008691:Methadone
Cost data; Economic evaluation; Missing data; Multiple imputation