INTERNAL AUDIT EFFECTIVENESS AND PROCUREMENT FRAUD DETECTION IN THE NIGERIAN PUBLIC SECTOR

Procurement fraud continues to undermine public financial management across many developing economies, with Nigeria's public sector being particularly vulnerable. This study examined the internal audit effectiveness and procurement fraud detection in the Nigerian Public Sector. Using a mixed-methods research design, the study draws on primary data collected from 280 respondents comprising internal auditors, procurement officers, finance managers, and audit committee members across 14 federal ministries, departments, and agencies (MDAs). Structured questionnaires and semi-structured interviews were employed for data collection, with quantitative data analysed using multiple regression and structural equation modelling (SEM), while qualitative data underwent thematic analysis. Findings reveal that internal audit effectiveness is a statistically significant predictor of procurement fraud detection (β = 0.389, p < 0.001). Audit independence exerts the strongest individual effect (β = 0.412, p < 0.001), followed by audit procedures (β = 0.321, p < 0.001), and Institutional barriers (β = 0.298, p < 0.01). Qualitative evidence consistently identifies political interference, inadequate staffing, insufficient use of technology, and weak enforcement of audit recommendations as critical barriers. Grounded in agency theory and fraud diamond theory, the study recommended that Constitutional and legislative entrenchment of internal audit independence. The Federal Government should amend the Financial Regulations and the Public Finance Management Act to require that Heads of Internal Audit report functionally to the Presidency and audit committees, and that their tenure protections are enshrined in legislation, not mere administrative circulars.