Does the effect of respondent characteristics on consumer assessments varyacross health plans?

Responses to the Consumer Assessments of Health Plans Survey (CAHPS(R)) are related to respondent characteristics. CAMPS procedures include casemix ad justment to remove effects of difference in respondent characteristics on c omparative plan ratings, under the assumption that casemix coefficients are homogeneous across plans. The authors analyzed data from the Washington st ate CAMPS demonstration,fitting hierarchical models in which coefficients o f casemix variables and intercepts could vary by plan. They estimated the i mpact of variability in casemix coefficients on plan adjustments and also a ssessed the implications for differential effects of individual characteris tics at different plans. Estimated between-plan variability of coefficients was small, but the data are consistent with substantially larger variabili ty. The potential impact of this variability on adjustments for plans was s mall relative to the magnitude of the adjustments. Comparisons between plan s for individuals, however, could be affected substantially. This methodolo gy could be useful wherever casemix adjustment is applied.