The online version of this article (https://doi.org/10.1186/s12874-018-0542-6) contains supplementary material, which is available to authorized users.
The original version of this article was revised: the notations Unit-nonresponse and Item-nonresponse should be used consistently.
A correction to this article is available online at https://doi.org/10.1186/s12874-018-0563-1.
Missing data can introduce bias in the results of randomised controlled trials (RCTs), but are typically unavoidable in pragmatic clinical research, especially when patient reported outcome measures (PROMs) are used. Traditionally applied to the composite PROMs score of multi-item instruments, some recent research suggests that multiple imputation (MI) at the item level may be preferable under certain scenarios.
This paper presents practical guidance on the choice of MI models for handling missing PROMs data based on the characteristics of the trial dataset. The comparative performance of complete cases analysis, which is commonly used in the analysis of RCTs, is also considered.
Realistic missing at random data were simulated using follow-up data from an RCT considering three different PROMs (Oxford Knee Score (OKS), EuroQoL 5 Dimensions 3 Levels (EQ-5D-3L), 12-item Short Form Survey (SF-12)). Data were multiply imputed at the item (using ordinal logit and predicted mean matching models), sub-scale and score level; unadjusted mean outcomes, as well as treatment effects from linear regression models were obtained for 1000 simulations. Performance was assessed by root mean square errors (RMSE) and mean absolute errors (MAE).
Convergence problems were observed for MI at the item level. Performance generally improved with increasing sample sizes and lower percentages of missing data. Imputation at the score and subscale level outperformed imputation at the item level in small sample sizes (n ≤ 200). Imputation at the item level is more accurate for high proportions of item-nonresponse. All methods provided similar results for large sample sizes (≥500) in this particular case study.
Many factors, including the prevalence of missing data in the study, sample size, the number of items within the PROM and numbers of levels within the individual items, and planned analyses need consideration when choosing an imputation model for missing PROMs data.
Additional file 1: Supplementary material for Multiple imputation for patient reported outcome measures in randomised controlled trials: advantages and disadvantages of imputing at the item, subscale or composite score level. Table S1. Overview of correlations between OKS outcome variables and covariates used in imputation models. Table S2. Overview of correlations between EQ-5D-3L outcome variables and covariates used in imputation models. Table S3. Overview of correlations between SF-12 outcome variables and covariates used in imputation models. Figures S1-S9. Supplementary graphs to Figs. 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12 in the manuscript, showing mean absolute errors instead of root mean square errors. (DOCX 1613 kb)
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- Multiple imputation for patient reported outcome measures in randomised controlled trials: advantages and disadvantages of imputing at the item, subscale or composite score level
Alastair M. Gray
David W. Murray
- BioMed Central
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