Further evidence supporting an SEM-based criterion for identifying meaningful intra-individual changes in health-related quality of life

This study used the standard error of measurement (SEM) to evaluate intra-i ndividual change on both the Chronic Respiratory Disease Questionnaire (CRQ ) and the SF-36. After analyzing the reliability and validity of both instr uments at baseline among 471 COPD outpatients, the SEM was compared to esta blished minimal clinically important difference (MCID) standards for three CRQ dimensions. A value of one SEM closely approximated the MCID standards for all CRQ dimensions. This SEM-based criterion was then validated by cros s-classifying the change status (improved, stable, or declined) of 393 foll ow up outpatients using the one-SEM criterion and the MCID standard. Excell ent agreement was achieved for all three CRQ dimensions. Although MCID stan dards have not been established for the SF-36, the one-SEM criterion was ex plored in these change scores. Among SF-36 scales demonstrating acceptable reliability and reasonable variance, the percent of individuals within each change category was consistent with those seen in the CRQ dimensions. Thes e results replicate previous findings where a value of one SEM also closely approximated MCIDs for all dimensions of the Chronic Heart Disease Questio nnaire among cardiovascular outpatients. The one-SEM criterion should be ex plored in other health-related quality of life instruments with established MCIDs. J CLIN EPIDEMIOL 52;9:861-873, 1999. (C) 1999 Elsevier Science Inc.