Differential item functioning by survey language among older Hispanics enrolled in Medicare managed care: a new method for anchor item selection.

OBJECTIVE: To propose a permutation-based approach of anchor item detection and evaluate differential item functioning (DIF) related to language of administration (English vs. Spanish) for 9 questions assessing patients' perceptions of their providers from the Consumer Assessment of Healthcare Providers and Systems (CAHPS) Medicare 2.0 survey. METHOD AND STUDY DESIGN: CAHPS 2.0 health plan survey data collected from 703 Hispanics who completed the survey in Spanish were matched on personal characteristics to 703 Hispanics that completed the survey in English. Steps to be followed for the detection of anchor items using the permutation tests are proposed and these tests in conjunction with item response theory were used for the identification of anchor items and DIF detection.

RESULTS: Of the questions studied, 4 were selected as anchor items and 3 of the remaining questions were found to have DIF (P < 0.05). The 3 questions with DIF asked about seeing the doctor within 15 minutes of the appointment time, respect for what patients had to say, and provider spending enough time with patients.

CONCLUSIONS: Failure to account for language differences in CAHPS survey items may result in misleading conclusions about disparities in health care experiences between Spanish and English speakers. Statistical adjustments are needed when using the items with DIF.