External Reserves and the Policy Trilemma in Nigeria: Reassessing Monetary Policy Independence under Exchange Rate and Capital Flow Constraints

Abstract

This study reassesses the role of external reserves in shaping Nigeria’s monetary policy independence within the framework of the policy trilemma, which highlights the inherent trade-offs among exchange rate stability, capital flow openness, and monetary autonomy. Using annual data from 1981 to 2023 and employing an Autoregressive Distributed Lag (ARDL) approach, the study explores how external reserves interact with exchange rate policies and capital mobility to influence Nigeria’s monetary autonomy. The study incorporates interaction effects to capture the conditional relationships between reserves and the other two legs of the trilemma. The model also incorporates key macroeconomic variables, including oil prices, inflation, financial development, and economic growth, to control for broader structural dynamics. Findings from the long-run analysis reveal that while external reserves are theoretically expected to enhance monetary policy independence, their effect is statistically insignificant, suggesting ineffective utilization. Exchange rate stability and capital mobility also show no significant long-run impact, indicating policy inconsistency and the limited effectiveness of Nigeria’s managed float regime and partial capital controls. Notably, oil price volatility emerges as the most significant determinant, with rising prices reducing the degree of monetary policy autonomy. Short-run dynamics reveal that reserves initially constrain policy independence but show a positive effect with lags, underscoring delayed policy transmission. Interaction terms between reserves and the trilemma components are also insignificant, suggesting that reserves have not functioned as a buffer against external constraints. Error correction estimates confirm that deviations from equilibrium are corrected rapidly, yet short-run dynamics reveal delayed and asymmetric policy effects. The findings underscore the need for a more coherent macroeconomic framework, improved reserve management, reduced oil dependency, and strengthened financial markets to enhance monetary policy independence in Nigeria.