Alternative analyses for handling incomplete follow-up in the intention-to-treat analysis: the randomized controlled trial of balloon kyphoplasty versus non-surgical care for vertebral compression fracture (FREE)

Abstract

Background: Clinical trial participants may be temporarily absent or withdraw from trials, leading to missing data. In intention-to-treat (ITT) analyses, several approaches are used for handling the missing information - complete case (CC) analysis, mixed-effects model (MM) analysis, last observation carried forward (LOCF) and multiple imputation (MI). This report discusses the consequences of applying the CC, LOCF and MI for the ITT analysis of published data (analysed using the MM method) from the Fracture Reduction Evaluation (FREE) trial.

Methods: The FREE trial was a randomised, non-blinded study comparing balloon kyphoplasty with non-surgical care for the treatment of patients with acute painful vertebral fractures. Patients were randomised to treatment (1:1 ratio), and stratified for gender, fracture aetiology, use of bisphosphonates and use of systemic steroids at the time of enrolment. Six outcome measures - Short-form 36 physical component summary (SF-36 PCS) scale, EuroQol 5-Dimension Questionnaire (EQ-5D), Roland-Morris Disability (RMD) score, back pain, number of days with restricted activity in last 2 weeks, and number of days in bed in last 2 weeks - were analysed using four methods for dealing with missing data: CC, LOCF, MM and MI analyses.

Results: There were no missing data in baseline covariates values, and only a few missing baseline values in outcome variables. The overall missing-response level increased during follow-up (1 month: 14.5%; 24 months: 28%), corresponding to a mean of 19% missing data during the entire period. Overall patterns of missing response across time were similar for each treatment group. Almost half of all randomised patients were not available for a CC analysis, a maximum of 4% were not included in the LOCF analysis, and all randomised patients were included in the MM and MI analyses. Improved estimates of treatment effect were observed with LOCF, MM and MI compared with CC; only MM provided improved estimates across all six outcomes considered.

Conclusions: The FREE trial results are robust as the alternative methods used for substituting missing data produced similar results. The MM method showed the highest statistical precision suggesting it is the most appropriate method to use for analysing the FREE trial data.

Trial registration: This trial is registered with ClinicalTrials.gov (number NCT00211211).

Figures

Figure 1

Missing data by treatment group in the Fracture Reduction Evaluation (FREE) trial. EQ-5D, EuroQol 5-dimension; RMD, Roland-Morris Disability; SF-36 PCS, short form-36 physical component summary.

Figure 2

Percentage reduction in standard error for all follow-up visits for six outcomes. Five outcomes assessed were: short form-36 physical component summary, EuroQol 5-dimension, Roland-Morris Disability, visual analogue scale and restricted activity. CC, complete case; LOCF, last observation carried forward; MI, multiple imputation; MM, mixed-effects model; SE, standard error.

Figure 3

Mean squared error for all follow-up visits for six outcomes, mean of the estimates from all 4 methods used as reference value. Five outcomes assessed were: short form-36 physical component summary, EuroQol 5-dimension, Roland-Morris Disability, visual analogue scale and restricted activity. CC, complete case; LOCF, last observation carried forward; MI, multiple imputation; MM, mixed-effects model; SE, standard error.

Figure 4

Percentage relative change in standard error for overall treatment effect in six outcomes. Six outcomes assessed were: short form-36 physical component summary, EuroQol 5-dimension, Roland-Morris Disability, visual analogue scale, restricted activity and days in bed. CC, complete case; LOCF, last observation carried forward; MI, multiple imputation; MM, mixed-effects model; SE, standard error.