The effect of macroeconomic variables on JSE size-based indices returns: Evidence from switching market conditions

The Johannesburg Stock Exchange (JSE) is considered a cornerstone of the South African economy, with its size-based indices serving as critical benchmarks for passive investment and portfolio construction. Although macroeconomic variables affect stock returns, the existing literature has primarily relied on linear models which yield heterogeneous results and do not allow for the dynamic and changing structure of financial markets. Consequently, this study investigates the nonlinear, regime-dependent effects of key macroeconomic variables such as inflation, money supply, short- and long-term interest rates, GDP, and the real effective exchange rate (REER) on the returns of the JSE Fledgling, Small-Cap, and Mid-Cap indices. Utilizing monthly data from 2002 to 2024, the study employs a two-state Markov Regime-Switching which allows the study to endogenously address the changes in bull and bear market regimes. The most pressing finding is that the Real Effective Exchange Rate (REER) is a consistently positive driver of returns across all market conditions, while the influences of other variables, such as interest rates and GDP growth, are highly dependent on the market regime (bull or bear) and the specific index size. Finally, these findings lead us to conclude that the relationship between macroeconomic fundamentals and stock returns is not a constant phenomenon but rather is fundamentally dependent on the regime, lending strong support for the Adaptive Market Hypothesis. This insight is significant for investors and portfolio managers, underscoring the necessity of adaptive, regime-sensitive strategies for effective risk management and portfolio allocation on the JSE.