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    Income stability, earnings volatility, and efficiency in Islamic banks: evidence from Sub-Saharan Africa
    (EJIF, 2026) Njogo, Michael Njoroge.; Dallu, Abdallah Mambo.; Korir, Fiona Jepkosgei.
    This study examines the relationship between earnings volatility and operational efficiency in Islamic banks in SSA, addressing a key methodological limitation in the Islamic banking efficiency literature. Conventional Data Envelopment Analysis (DEA), widely used in prior studies, produces upward-biased efficiency scores and invalid second-stage inference when efficiency is linked to stochastic variables such as earnings volatility. This limitation is particularly consequential in Islamic banking, where income streams are structurally volatile due to profit-and-loss sharing and asset-backed financing arrangements. Methodologically, this study demonstrates the necessity of bias correction and applies the Simar–Wilson two-stage DEA framework to obtain statistically valid efficiency–volatility estimates. Using a balanced panel of fully-fledged Islamic banks in SSA from 2010 to 2024, operational efficiency is measured as income-generation efficiency based on non-interest revenue streams. First, operational efficiency is estimated under alternative returns-to-scale assumptions using non-interest operating expenses as inputs and Shariah-compliant non-interest income components as outputs. In the second stage, bias-corrected efficiency scores are regressed on earnings volatility—measured as the rolling standard deviation of return on assets (ROA), which captures earnings volatility relative to asset utilization and aligns with operational efficiency—using truncated regression with bootstrapping. The results reveal a statistically significant negative relationship between earnings volatility and operational efficiency, indicating that earnings volatility weakens Islamic banks’ capacity to efficiently transform operating costs into Shariah-compliant income. Robustness checks confirm the stability of the findings across efficiency specifications. Beyond its empirical contribution, the study shows that efficiency levels reported in prior Islamic banking studies relying on conventional DEA may be systematically overstated in volatile-income environments, with important implications for supervision and policy in emerging Islamic finance markets.
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    Capital adequacy, risk absorption, and operational efficiency of Islamic in sub-Saharan Africa
    (University of Turin, 2026) Njogo, Michael Njoroge.; Korir, Fiona Jepkosgei.; Dallu,Abdallah Mambo.
    Abstract This study examines how capital adequacy shapes the operational efficiency of Islamic banks in Sub-Saharan Africa (SSA), with particular emphasis on its role as an internal risk-absorption mechanism rather than a purely prudential stability buffer. Despite its central role in Islamic banking regulation, the efficiency implications of capital adequacy, particularly in developing and institutionally constrained Islamic finance markets, remain largely unexplored. Based on a balanced panel of fully-fledged Islamic banks in SSA from2010to 2024, the paper employs a two-step empirical approach. Bias-corrected operational efficiency scores are estimated in the first stage using the Simar–Wilson two-stage Data Envelopment Analysis (DEA) framework. In the second stage, we explore the non-linear effects of capital adequacy on efficiency using panel regression techniques, controlling for bank-specific and institutional factors. To address endogeneity, persistence, and reverse causality, a dynamic panel model is estimated using System GMM as a robustness check. The findings indicate non-linear relationship between capital adequacy and operational efficiency. Moderate capital buffers are associated with improved efficiency through higher loss absorption capacity and stabilisation of operating costs, while excessive capitalisation is accompanied by scale inefficiencies and less effective intermediation. These results indicate that Islamic banking exhibits an efficiency trade-off in capital adequacy, as prudential strength beyond an optimal level may limit productivity in resource allocation. The study makes an important contribution to Islamic banking literature by reframing capital adequacy as a channel of structural efficiency and by providing rare dynamic evidence from SSA. This raises policy implications and suggests the need for commensurate capital calibration that balances prudential resilience against operational efficiency for emerging Sharīʿah-compliant banking systems.