Analysis of change in patient reported outcome measures with floor and ceiling effects using the multi-level Tobit model: A simulation study and an example from a National Joint Register using body mass index and the Oxford Hip Score

Adrian E Sayers*, Michael R Whitehouse, Andrew Judge, Alexander MacGregor, Ashley W Blom, Yoav Ben-Shlomo

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)

Abstract

Objectives
This study has three objectives. 1) Investigate the association between body mass index (BMI) and the efficacy of primary hip replacement using a Patient Reported Outcome Measure (PROMs) with a measurement floor and ceiling. 2) Explore the performance of different estimation methods to estimate change in PROMs score following surgery using a simulation study and real word data where data has measurement floors and ceilings. 3) Lastly, develop guidance for practicing researchers on the analysis of PROMs in the presence of floor and ceiling effects.

Design
Simulation study and prospective national medical device regiseter

Setting
National register of joint replacement and medical devices

Methods
Using a Monte-Carlo simulation study and data from a national joint replacement register (162,513 patients with pre/post surgery PROMs) we investigate simple approaches for the analysis of outcomes with floor and ceiling effects that are measured at two occasions: linear and Tobit regression (baseline adjusted ANCOVA, change-score analysis, post-score analysis) in addition to linear and multi-level Tobit models.

Primary outcome
The primary outcome of interest is change in patient reported outcome measures from pre-surgery to 6 months post-surgery.

Results
Analysis of data with floor and ceiling effects with models that fail to account for these features induce substantial bias. Single level Tobit models only correct for floor or ceiling effects when the exposure of interest is not associated with the baseline score. In observational data scenarios, only multi-level Tobit models are capable of providing unbiased inferences.

Conclusions
Inferences from pre/post studies that fail to account for floor and ceiling effects may induce spurious associations with substantial risk of bias. Multi-level Tobit models indicate the efficacy of total hip replacement is independent of BMI. Restricting access to total hip replacement based on a patients BMI can not be supported by the data.
Original languageEnglish
JournalBMJ Open
Publication statusAccepted/In press - 26 Jun 2020

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