Core Outcome Measures Index
https://orthotoolkit.com/comi-back/
The Oswestry Disability Index (ODI) and the Core Outcome Measures Index (COMI) are two commonly used self-rating outcomes instruments in patients with lumbar spinal disorders.
The core outcome measures index (COMI) for the back is a questionnaire that evaluates five domains and has been translated into several languages and validated for different populations. Valente Aguiar et al. aimed to translate, cross-culturally adapt, and validate it in European Portuguese for use in patients with degenerative lumbar disease. Additionally, we aimed to establish the minimal clinically important change score (MCIC).
The translation and cultural adaptation were done according to published guidelines. Patients awaiting surgery at a neurosurgical center completed the COMI, Oswestry Disability Index (ODI), EQ-5D questionnaires, and a pain visual analog scale (VAS). To evaluate COMI's reproducibility, patients completed the questionnaire twice within two weeks, preoperatively, in addition to answering a transition question. The MCIC was determined by analysis of postoperative changes in total COMI score, using the anchor method, with a question ascertaining surgical outcome as perceived by the patient.
The first set of questionnaires was answered by 108 patients and the second, by 98 patients. COMI's construct validity was confirmed by demonstrating the hypothesized correlation between each domain's score (Spearman Rho > 0.4) and the corresponding questionnaire score (ODI, EQ-5D, and VAS) and through adequate correlation (Spearman > 0.6) between COMI's total score and ODI and EQ-5D total scores. Intraclass correlation coefficients between each domain and COMI's total score were > 0.8. The MCIC was calculated as 2.1.
The cross-culturally adapted COMI questionnaire is a valid clinical assessment tool for European Portuguese-speaking patients with degenerative lumbar disease, with an MCIC of 2.1 points 1).
No formal crosswalk between them exists that would otherwise allow the scores of one to be interpreted in terms of the other. Mannion et al. aimed to create such a mapping function.
They performed a secondary analysis of ODI and COMI data previously collected from 3324 patients (57 ± 17y; 60.3% female) at baseline and 1y after surgical or conservative treatment. Correlations between scores and Cohen's kappa for agreement (κ) regarding the achievement of the minimal clinically important change (MCIC) score on each instrument (ODI, 12.8 points; COMI, 2.2 points) were calculated, and regression models were built. The latter was tested for accuracy in an independent set of registry data from 634 patients (60 ± 15y; 56.8% female).
Results: All pairs of measures were significantly positively correlated (baseline, 0.73; 1y follow-up (FU), 0.84; change-scores, 0.73). MCIC for COMI was achieved in 53.9% of patients and for ODI, in 52.4%, with 78% agreement on an individual basis (κ = 0.56). Standard errors for the regression slopes and intercepts were low, indicating excellent prediction at the group level, but root means square residuals (reflecting individual error) was relatively high. ODI was predicted as COMI × 7.13-4.20 (at baseline), COMI × 6.34 + 2.67 (at FU), and COMI × 5.18 + 1.92 (for change-score); COMI was predicted as ODI × 0.075 + 3.64 (baseline), ODI × 0.113 + 0.96 (FU), and ODI × 0.102 + 1.10 (change-score). ICCs were 0.63-0.87 for derived versus actual scores.
Conclusion: Predictions at the group level were very good and met standards justifying the pooling of data. However, we caution against using individual values for treatment decisions, e.g. attempting to monitor patients over time, first with one instrument and then with the other, due to the lower statistical precision at the individual level. The ability to convert scores via the developed mapping function should open up more centers/registries for collaboration and facilitate the combining of data in Meta-analysis 2).