An Investigation of Differential Item Functioning in the Infection Control Contact Isolation Precaution Instrument Among Nurses and Physicians.

OBJECTIVE: Healthcare workers must understand disease transmission and adhere to appropriate precautions to prevent infections. However, differences in how questionnaire items are interpreted may lead to misleading comparisons between groups of healthcare professionals. This study examines differential item functioning (DIF) in the contact isolation precautions questionnaire between nurses and physicians. METHODS: In this cross-sectional study, 676 nurses and 138 physicians completed the questionnaire in May 2019. DIF was assessed using Firth binary logistic regression. RESULTS: Among the 814 participants, 83% were nurses and 17% were physicians. DIF analysis identified item 8 in the knowledge domain as significant. After its removal, mean scores between the two groups remained significantly different (p < 0.001). In the attitude domain, removing Items 6 and 8 eliminated significant score differences. However, in the practice domain, mean score differences persisted even after removing Items 2, 3, and 6 individually or together (p < 0.001). Nurses consistently scored higher in all domains. CONCLUSION: Nurses and physicians may interpret some items of the contact isolation precautions questionnaire differently, which may affect comparisons of knowledge, attitude, and practice scores. Therefore, measurement equivalence should be considered when comparing these groups. These findings are specific to the questionnaire and study population examined and should not be generalized to other infection prevention and control instruments or populations. Further multicenter studies are warranted. IMPLICATIONS FOR NURSING PRACTICE: Differences in item functioning should be considered when comparing nurses and physicians using this questionnaire. Despite relatively high knowledge and attitude scores, practice scores remained low, particularly among physicians, highlighting the importance of considering measurement equivalence when interpreting these differences and planning educational strategies.