Imputation of ordinal outcomes: a comparison of approaches in Traumatic Brain Injury

Kunzmann, K.; Wernisch, L.; Richardson, S.; Steyerberg, E.W.; Lingsma, H.; Ercole, A.; ... ; Wilson, L. (2020)

Article / Letter to editor

Loss to follow-up and missing outcomes data are important issues for longitudinal observational studies and clinical trials in traumatic brain injury. One popular solution to missing 6-month outcomes has been to use the last observation carried forward (LOCF). The purpose of the current study was to compare the performance of model-based single-imputation methods with that of the LOCF approach. We hypothesized that model-based methods would perform better as they potentially make better use of available outcome data. The Collaborative European NeuroTrauma Effectiveness Research in Traumatic Brain Injury (CENTER-TBI) study (n = 4509) included longitudinal outcome collection at 2 weeks, 3 months, 6 months, and 12 months post-injury; a total of 8185 Glasgow Outcome Scale extended (GOSe) observations were included in the database. We compared single imputation of 6-month outcomes using LOCF, a multiple imputation (MI) panel imputation, a mixed-effect model, a Gaussian process regression, and a multi-state model. Model performance was assessed via cross-validation on the subset of individuals with a valid GOSe value within 180 +/- 14 days post-injury (n = 1083). All models were fit on the entire available data after removing the 180 +/- 14 days post-injury observations from the respective test fold. The LOCF method showed lower accuracy (i.e., poorer agreement between imputed and observed values) than model-based methods of imputation, and showed a strong negative bias (i.e., it imputed lower than observed outcomes). Accuracy and bias for the model-based approaches were similar to one another, with the multi-state model having the best overall performance. All methods of imputation showed variation across different outcome categories, with better performance for more frequent outcomes. We conclude that model-based methods of single imputation have substantial performance advantages over LOCF, in addition to providing more complete outcome data.

• GOSe
• imputation
• missing data
• traumatic brain injury

• All authors: Kunzmann, K.; Wernisch, L.; Richardson, S.; Steyerberg, E.W.; Lingsma, H.; Ercole, A.; Maas, A.I.R.; Menon, D.; Wilson, L.
• Date: 2020-11-13
• Journal: Journal of Neurotrauma
• Volume: 38
• Issue: 4
• Pages: 455 - 463
• DOI: doi:10.1089/neu.2019.6858
• Link: https://www.liebertpub.com/doi/10.1089/neu.2019.6858