Capital Market Seasonality: The Case of Bond Returns

The existence of seasonality in security rates of return has implications for both the study of market efficiency and tests involving return models. The existence of seasonal asset returns may be an indicator of market inefficiencies. In an efficient market, investor arbitrage should remove any excess seasonal return an asset receives over a comparable asset of equal risk. The presence of seasonal returns, however, does not necessitate market inefficiency. For example, an expected seasonal return may exist in an efficient market simply because of anticipated seasonal patterns embedded in its underlying determinants. Tax regulations, government monetary policy, seasonal information lags, or risk adjustments have all been advanced as determinants of seasonal movements in return. No matter what the basis for return seasonality or the extent of market efficiency, if seasonality in asset returns exists, then these returns do not follow a strict stationary process within the year. Statistical models analyzing asset returns may use this information to improve model specification. For instance, Kinney and Rozeff [16] have shown that large efficiency gains in estimating portfolio betas can be achieved using time stratified estimates which explicitly incorporate seasonality in 4 stock returns.