Understanding the Cap Size Premium

For some reason, the small cap premium keeps coming up. It is one of the original Fame-French Factors and continues to persist, even after tall of these decades.

However, if you really want to see premia based on size, there must also be a control for quality. Here is Cliff Asness of AQR explaining the issue with size:

The size premium has been challenged along many fronts: it has a weak historical record, varies significantly over time, in particular weakening after its discovery in the early 1980s, is concentrated among microcap stocks, predominantly resides in January, is not present for measures of size that do not rely on market prices, is weak internationally, and is subsumed by proxies for illiquidity. We find, however, that these challenges are dismantled when controlling for the quality, or the inverse “junk”, of a firm. A significant size premium emerges, which is stable through time, robust to the specification, more consistent across seasons and markets, not concentrated in microcaps, robust to non-price based measures of size, and not captured by an illiquidity premium. Controlling for quality/junk also explains interactions between size and other return characteristics such as value and momentum.


Size Matters, If You Control Your Junk