Short-term interest rate processes affect how interest rates are set in South Africa. Researchers studied different models to see which one best fits the data. They found that models where interest rate volatility changes with the interest rate level work best, especially after inflation targeting was introduced. Models with restrictions that don't allow for this effect or set it too high don't match the data well. The specific way the interest rate changes over time didn't seem to make a difference in how well the models fit the data.