ANOMALY, generally, is a deviation from the common rule. It is an irregularity that is difficult to explain using existing rules or theory. In securities, it is an unexplained or unexpected price or rate relationship that seems to offer an opportunity for an arbitrage-type profit, although not typically without risk. Examples include the tendency of small stocks to outperform large stocks, of stocks with low price-to-book value ratios to outperform stocks with high price-to-book value ratios, and of discount currency forward contracts to outperform premium currency forward contracts.
