A Differential Item Functioning (DIF) Study of the Infection Control Standard Isolation Precaution Instrument Across Gender and Major Among Healthcare Workers

Background: Measuring healthcare workers’ (HCWs) knowledge, attitudes, and practices (KAPs) regarding isolation precaution is essential for infection control which needs a valid and reliable instrument. Objectives: This study aimed to assess differential item functioning (DIF) across gender and major for the knowledge and practice items of the questionnaire, previously designed in Shiraz, Iran. Methods: This cross-sectional survey was conducted on 1070 participants (males/females: 306/764; medical students/nurses: 466/624). The study instrument had three subscales with nine questions for each KAP subscale. The Mantel-Haenszel (MH) statistic was used. The DIF and differential test functioning (DTF) analyses were also performed in this study. Results: There were very similar DIF outcomes for the knowledge and practice subscales, with one or two items indicating moderate DIF but comparable total scores across genders. Across majors, several items showed large DIF for both subscales. It was found that large DTF affects major for both subscales. Conclusions: Our findings indicated large DIF and DTF levels of the questionnaire among medical students and nursing groups. More attention should be paid when developing the items. This study shows the importance of paying attention to valid evidence for instruments developed within the field of healthcare.