The Oort structural equation modeling approach detected a response shift after a COPD self-management program not detected by the Schmitt technique.

ABSTRACT

OBJECTIVE: If individuals experience a response shift, scores on measures before and after a self-management intervention may not be comparable. This study evaluated whether persons with chronic obstructive pulmonary disease (COPD) experience a response shift after participating in a self-management program. The second objective was to compare the Oort and Schmitt structural equation modeling (SEM) approaches. METHODS: Secondary analyses from a randomized controlled trial comparing a home- and hospital-based pulmonary rehabilitation program were used to assess response shift on a physical and mental health-measurement model measured using the Chronic Respiratory Questionnaire (CRQ) and the St. George's Respiratory Questionnaire (SGRQ) over a 1-year period. RESULTS: The Oort approach showed significant changes between the no response shift model and models removing invariance constraints for the residual of the CRQ dyspnea (chi(2)(SBdiff)=7, df=1) (uniform recalibration) and intercepts of the SGRQ activity (chi(2)(SBdiff)=14, df=1) and impact (chi(2)(SBdiff)=10, df=1) subscales (nonuniform recalibration). Change in factor means showed changes in the physical health factor, which was slightly lower in unadjusted (0.32) as compared with the response shift-adjusted model (0.40). The Schmitt procedure was not supportive of any response shift effect and showed a marginal change in random error over time. CONCLUSIONS: This study showed that COPD patients experienced a response shift after participating in a self-management program, which resulted in an underestimation of change in physical health. These results suggest that the Oort procedure is more sensitive in detecting a response shift, and that a measurement of response shift is needed before results can be interpreted. Future comparisons with other methods and a control group are needed.