Board Characteristics, Ownership Structure, and Shareholder Activism as Determinants of Sustainability Transparency: Panel Data Analysis for Türkiye

Using data from the 41 companies listed on the Borsa Istanbul Sustainability Index between 2020 and 2024, this study examines the relationship between board characteristics, concentrated ownership structure, shareholder activism and sustainability transparency. Reports published on a voluntary basis were subjected to content analysis based on criteria selected from the Global Reporting Initiative (GRI) standards, and a sustainability disclosure score was calculated. The relationship between board characteristics, concentrated ownership structure, shareholder activism, financial metrics identified as control variables, and sustainability scores was evaluated via robust random effects (static) and System Generalized Method of Moments (System GMM) (dynamic) panel data estimators. According to the static estimation results, board meeting frequency and the ratio of female members serve as positive drivers for sustainability transparency. In the dynamic model estimates, these governance mechanisms lose their explanatory power and show no statistically observable effect. However, across both methodological approaches, firm size, which was integrated as a control factor, consistently demonstrates a robust positive correlation with levels of disclosure. These findings reveal that governance mechanisms such as the percentage of female members and meeting frequency have a short-term and marginal effect, but structural factors such as company size are the main determinants for a long-term and sustainable level of transparency in Türkiye. Consequently, market regulators should deploy policy frameworks that incentivize disclosure trajectories aligned with international frameworks while fostering voluntary reporting. Concurrently, corporate managers should look beyond mere statutory compliance and continuously embrace extensive global reporting standards.