Validation of a consensus-based minimal clinically important difference (MCID) threshold using an objective functional external anchor

Background contextThe minimal clinically important difference (MCID) is defined as the smallest change in an outcome that a patient would perceive as meaningful. The Initiative on Methods, Measurement and Assessment in Clinical Trials (IMMPACT) group proposed defining the MCID as a 30% improvement in self-reported pain or function. However, this MCID threshold has not been validated against an objective physical measure.PurposeTo test the validity of the IMMPACT-based MCID threshold, using an objective physical measure as an external anchor.Study design/settingProspective study of chronic disabling occupational lumbar disorder (CDOLD) patients completing a functional restoration program.Patient sampleA consecutive cohort of 743 CDOLD patients.Outcome measuresSelf-report measures of pain-related function were compared with an objective lifting measure, the progressive isoinertial lifting evaluation (PILE), obtained after treatment.MethodsThe association between reporting 30% or greater improvement (the IMMPACT's MCID key criterion) and the PILE score after treatment was assessed.ResultsA 30% or greater improvement on the self-report measures was significantly associated with improvement in physical function on the PILE task.ConclusionsDespite extensive use of the MCID to evaluate effects of treatment in spinal disorders, this is the first empirical documentation of the validity of the IMMPACT's 30% change criterion compared with an objective physical anchor.