This study investigates the relationship between sustainability reporting assurance (SRA) and the stock market performance of firms listed on the Nigerian Exchange Group (NGX) over the period 2010–2024. Drawing on legitimacy theory, stakeholder theory, and signalling theory, the research examines whether third-party assurance of sustainability reports enhances investor confidence and, ultimately, market valuation. The study employs an ex-post facto research design with panel regression analysis on a sample of 151 listed firms across fifteen reporting years. Stock market performance is proxied by Tobin's Q and market-to-book ratio, while sustainability reporting assurance is measured through a composite index capturing the scope, provider, and level of assurance obtained. Seven control variables—firm size, firm age, board size, board independence, industry type, financial leverage, and ownership structure—are incorporated to isolate the effect of SRA on market performance. Descriptive statistics, correlation analysis, and post-estimation diagnostics, including the Hausman test, Breusch-Pagan Lagrange Multiplier test, variance inflation factor analysis, and the Wooldridge test for serial autocorrelation, are conducted. The findings reveal a statistically significant positive relationship between sustainability reporting assurance and stock market performance, indicating that assured sustainability disclosures serve as credible signals that reduce information asymmetry and improve market valuation. Board independence and firm size also emerge as significant predictors. The study contributes to the nascent literature on sustainability assurance in emerging markets, offering practical implications for regulators, corporate boards, and assurance providers in Nigeria. It recommends mandatory assurance frameworks for sustainability disclosures among listed firms to strengthen market integrity and attract sustainable investment.
Onipe Adabenege Yahaya (Sun,) studied this question.