Regret theory and the banking firm: The optimal bank interest margin

This paper examines the optimal bank interest margin, i.e., the spread between the loan rate and the deposit rate of a bank, when the bank is not only risk-averse but also regret-averse. Regret-averse preferences are characterized by a utility function that includes disutility from having chosen ex-post suboptimal alternatives. We show that the presence of regret aversion raises or lowers the optimal bank interest margin than the one chosen by the purely risk-averse bank, depending on whether the probability of default is below or above a threshold value, respectively. Regret aversion as such makes the bank less prudent and more prone to risk-taking when the probability of default is high, thereby adversely affecting the stability of the banking system.