ENGLISH ABSTRACT: Experimental research in psychology and economics indicates that depression causes heightened risk aversion. Previous research has documented robust links between seasonal variation in length of day, seasonal depression (known as seasonal affective disorder, or SAD), risk aversion and stock market returns. One such study provides international evidence that stock market returns vary seasonally with the length of the day, a result called the SAD effect. Stock returns are shown to be significantly related to the amount of daylight throughout the autumn and winter. Another study examines the SAD effect in the context of an equilibrium asset pricing model to determine whether the seasonality can be explained using a conditional version of the capital asset pricing model (CAPM) that allows the price of risk to vary over time.Given the above as the base departure point, this report analyses the SAD effect in the context of the South African capital market, where, firstly, the variation in length of day during the year is not so severe compared with other countries like Sweden and the UK and, secondly, a more recent dataset includes the effects of integrated markets and globalisation, that possibly resulted in a shift of seasonal behaviour in the market. It quantifies the SAD effect in general, across industry sectors, over time periods and confirms that a conditional CAPM holds in explaining the seasonality due to SAD.The results differ substantially from those of prior studies. The expected signs of the SAD and Aut coefficients are reversed. Closer analysis shows that seasonality in stock returns has undergone a shift compared to seasonality in an older dataset.A prior finding that effects, such as the SAD, are better explained using excess returns than using raw total returns of the market, is reinforced.The analysis of SAD over time sheds some light on the unexpected outcome of the SAD and Aut coefficients by providing evidence that the validity of regression models deteriorated over time and, more conclusively, that in two consecutive periods, the SAD and Aut coefficients decreased in absolute value. It also found that the coefficients are linearly related to excess returns during the latter period only.The conditional CAPM provides evidence that the effect of SAD is captured in the time variation in the price of risk. The factor of reducing the remainder of SAD in error terms is, however, remarkably smaller. The implication is that market risk already accounts for the SAD effect, but only to a degree, and that the remaining contribution of the SAD effect contained in varying theprice of risk is substantially less significant. This finding coupled with the contradictory results in the signs of SAD and Aut coefficients renders evidence of SAD in the South African market rather inconclusive.
