Differential use of the CAHPS® 0–10 global rating scale by medicaid and commercial populations

The primary objective of this study was to investigate whether Medicaid managed care enrollees and commercially insured health plan participants respond differently to the CAHPS® 2.0 health plan survey global ratings of health care, personal doctor or nurse, and health plan. A secondary objective was to examine whether and how these differences may vary by alternative approaches to collapsing the 0-10 response scale. This study is a secondary analysis of CAHPS 2.0 health plan survey data collected in 1999 and 2000. Data on 2,142 Iowa Medicaid managed care enrollees and 1,051 commercially insured State of Iowa employees were analyzed. Differences in responses between the Medicaid-enrolled and commercially insured respondents were modeled using multinomial logistic regression, adjusting for demographics, health status and CAHPS composite measures. Results of these analyses indicated that Medicaid enrollees were significantly more likely than State of Iowa employees to use the extreme ends of the CAHPS global rating scales, particularly in the approaches when the category representing the highest end of the scale was defined as a score of 10 for the analysis. Thus, the choice of cut points for collapsing the 0-10 scales influenced statistical differences on CAHPS global ratings of care, doctor and health plan between Medicaid and privately insured populations. In conclusion, a populations use of the extremes of the global rating scales should be considered when comparing or combining CAHPS data for different populations. If response contraction bias is present, a format such as the alternative approach presented here (using categories 0-4, 5-8, 9, 10) that captures that bias may be preferable to the CAHPS format, which has been shown to maximize plan differentiation.