Exploring response shift in longitudinal data

OBJECTIVE : To evaluate recall bias in the thentest and to explore response shifts in chronically ill patients over time. METHODS : In a five-year study of 93 multiple sclerosis patients, kappa statistics examined recall bias in thentest scores. The thentest examined changes in internal standards. Longitudinal factor analysis investigated changes in conceptualization in evaluating quality of life (QOL). RESULTS : Standard analyses revealed deteriorating physical role performance but stability in other QOL indicators over time. Agreement between baseline indicators and thentest scores was lower for fatigue than for ambulation ( p <0.02), suggesting that the thentest captures recalibration response shift (17%) along with recall bias (22%). Patients changed internal standards for physical role limitations ( p <0.05) and fatigue ( p <0.0001), and reconceptualized QOL with respect to well-being and physical role. CONCLUSIONS : Underlying response shifts allowed patients to maintain homeostasis in reported QOL despite physical deterioration. These shifts interrelate but are not redundant. More variance in the thentest was explained by recall bias than by recalibration response shift