Corporate Board Diversity, Agency Costs, and Firm Value: Evidence from Listed Companies on the Nigerian Stock Exchange

This study empirically investigates the effects of corporate board diversity, measured along gender, educational background, and independence dimensions, on agency costs and firm value among companies listed on the Nigerian Stock Exchange. Board diversity has attracted considerable theoretical debate, but empirical evidence from Nigeria's capital market remains fragmented, particularly regarding the agency cost transmission mechanism. This research employs a longitudinal quantitative design using secondary panel data for 60 listed firms over a five-year period. Fixed effects regression and two-stage least squares estimation were used to address potential endogeneity concerns. Findings reveal that gender diversity and board independence are associated with statistically significant reductions in agency costs, proxied by asset utilisation ratio and expense ratio, and positive effects on Tobin's Q as a firm value measure. Educational diversity on boards shows positive associations with strategic decision quality but weaker direct effects on firm value. The study fills an identified research gap by demonstrating that agency cost reduction partially mediates the diversity-firm value relationship, adding nuance to existing governance literature. Results have direct implications for regulatory reforms targeting board composition requirements in Nigerian capital markets. The study recommends that the Securities and Exchange Commission strengthen diversity disclosure requirements and promote independent director development programmes. Keywords: board diversity, agency costs, firm value, Nigerian Stock Exchange, corporate governance.