Voluntary Sustainability Assurance and Market Uncertainty: Evidence From Türkiye

ABSTRACT This study examines whether voluntary sustainability assurance is associated with lower market uncertainty in an emerging market undergoing a transition towards mandatory sustainability assurance. Using 383 firm‐year observations for 80 non‐financial firms in Türkiye during 2019–2024, restricted to firm‐years in which assurance remained voluntary, firm and year fixed‐effects regressions examine stock return volatility and market illiquidity. Additional analyses consider firm‐size heterogeneity, Big 4 auditor quality, stricter assurance coding, propensity‐score matching, endogeneity concerns and the pre‐mandate 2019–2023 period. Voluntary sustainability assurance is not systematically associated with lower volatility or illiquidity, while size‐ and auditor‐quality interactions are insignificant. The main inference is preserved in the pre‐mandate subsample and alternative robustness tests. The findings suggest that assurance adoption alone may not provide a sufficiently comparable or interpretable signal to influence market learning, highlighting a credibility‐accountability gap between assurance adoption and observable market outcomes.