Uncovering potential interviewer-related biases in self-efficacy assessment: a study among chronic disease patients

Abstract Background Self-efficacy refers to an individual's belief in their ability to accomplish specific tasks and achieve goals, and plays an essential role in achieving positive outcomes in a wide range of domains. Central to the measurement of any form of self-efficacy is the assessment without bias, also in case of an interview situation. Methods Outpatients with macular edema, an eye disease, participated in this questionnaire-based cross-sectional study. The study assessed self-efficacy using the General Self-Efficacy Scale (GSE) in German. Interviewers read questionnaires aloud to patients. Differential item functioning (DIF) was investigated using likelihood-ratio χ2 tests for interviewer, sex, age, education, working status, income, diagnosis, and health-status. Results The analysis included N = 556 patients. Median age was 68.4 (IQR: 62.0 – 76.0) years and mean overall GSE score 32.8 (SD: 4.81). No DIF was detected for interviewer. However, DIF was found in item 1 for education (uniform DIF, NCDIFno degree vs. degree = 0.042; easier with degree vs. none), in item 1 and 3 for income (item 1: non-uniform DIF, NCDIF<€ 1,125 vs.≥€ 1,125≤€ 1,950 = 0.050 / NCDIF< € 1,125 vs.≥€ 1,950 = 0.099; item 3: uniform DIF, NCDIF<€ 1,125 vs.≥€ 1,125—≤€ 1,950 = 0.024 / NCDIF< € 1,125 vs.≥€ 1,950: 0.095; both easier with higher income), in item 2 for working status (uniform DIF, NCDIFretired vs. other = 0.017; easier if working) and in item 3 for sex (non-uniform DIF, NCDIFmale vs. female = 0.043; easier for women in low ability, harder for them from medium ability on). Conclusions Given that no DIF was detected concerning interviewers, our findings indicate that an objective assessment of self-efficacy in a face-to-face interview may be feasible, provided that interviewers receive appropriate training. Since DIF effects concerning other patients characteristics found were small, the GSE may provide a relatively bias free way to assess self-efficacy in an interview setting