Factor Models May Work Because Everyone Uses the Same Models
Gerber disputes the significance assigned to sprawling factor systems, arguing that market and sector explain most of what is defensibly factor-driven. He says widespread use of the same models can push prices into alignment during normal periods, creating behavior that appears to validate the models until a dislocation arrives.
- Many additional factors explain little incremental movement
- Leverage can exaggerate the apparent importance of weak effects
- Shared models can make markets conform temporarily to their assumptions
- A trading signal model should not automatically become a risk model
“Six percent of a stock price movement can be explained by twenty one factors”
“everyone's using basically the same factor models. It pushes things in alignment, which works in normal market environments.”