Empirical Investigation of Source Credibility and Its Effect on Attitude Change in Nigerian Health Communication

Source credibility is a foundational concept in persuasion research, and its role in health communication attitude change has significant implications for the design of effective public health messaging in Nigeria's complex media and social authority environment. This study empirically investigated the effects of source credibility dimensions on attitude change toward health behaviours in Nigerian audiences. A 2x2 factorial experiment was conducted with 240 adult participants in Kano and Ibadan, manipulating source expertise (medical professional versus celebrity) and source trustworthiness (high versus low, varied through vested interest disclosure) for messages about antibiotic resistance awareness. Pre- and post-message attitude change was measured using a validated health attitude scale. Results showed significant main effects of both expertise (F = 18.4; p < 0.001) and trustworthiness (F = 22.7; p < 0.001) on attitude change, with a significant interaction effect. The combination of high expertise and high trustworthiness produced the largest attitude change. Notably, the celebrity source with high trustworthiness achieved attitude change comparable to the medical professional with high trustworthiness among participants with low health literacy. Religious authority was identified in post-test open responses as a credibility dimension absent from the experimental design but highly relevant for northern Nigerian participants. The study provides original experimental evidence on source credibility in Nigerian health communication, identifying religious authority as a critical under-researched credibility dimension for northern Nigerian health messaging contexts. Keywords: source credibility, health communication, attitude change, persuasion, Nigeria