The interrelationship between net interest margin and non-interest income: Evidence from Vietnam

Purpose: The purpose of this paper is to investigate the interrelationship between non-interest income (NII) and net interest margin (NIM) in the Vietnamese banking system between 2006 and 2015. Thereafter, the impact of NII on risk-adjusted returns is also examined.

Design/methodology/approach: Various analysis techniques are used to achieve the research objectives.

Findings: The findings show a negative two-way link between NII and NIM, thus supporting the subsidisation hypothesis. Furthermore, NII is found to have a negative impact on risk-adjusted returns. When observing this relationship in sub-samples, the findings indicate that the negative impact of NII on risk-adjusted returns still holds in the first subsample (2006-2011). The coefficient of NII becomes positive but not significant for the subsequent period (2012-2015). In addition, the Spearman rank-order correlations of returns on assets and NII for both sub-samples are negative. Together, the author concludes that there are no diversification benefits in the Vietnamese banking system.

Practical implications: The evidence suggests a trade-off between non-interest activities and traditional lending ones. In addition, the findings demonstrate that the Vietnamese banks may use NIIs to expand leverage and herd by coordinating NII strategy during the economic downturns. Thus, the banking system may be exposed to a greater risk. The research has implications for bank supervisors, policy-makers and bank managers.

Originality/value: This study is the first attempt to investigate the interrelationships between net NII and NIM in the Vietnamese banking system.