Three-Rationale Factor Durability Test
Explain factor persistence through risk, constraints, or behavior
- Difficulty
- Moderate
- Time to result
- ~weeks to results
- Steps
- 5
- Confidence
- 97%
The test asks why a factor's excess return has not been arbitraged away and requires at least one of three durable explanations. A risk rationale means investors earn compensation for bearing losses in difficult states, as value investors may during late-cycle contractions. A structural rationale arises when mandates, leverage limits, return targets, or other institutional rules force market participants into predictable positions, potentially sustaining effects such as minimum volatility. A behavioral rationale rests on recurring human biases that do not vanish merely because research exposes them. The analyst identifies the counterparty, names the mechanism, and considers what would have to change for it to disappear. A factor supported by no credible rationale is treated skeptically; one dependent on a removable constraint requires active monitoring.
Origin
Extracted from Masters in Business during Andrew Ang's explanation of why established factors have not simply been arbitraged away.
Core principles
- 01Every persistent factor needs an economic counterparty
- 02Risk-bearing can earn compensation through uncomfortable cycles
- 03Institutional constraints can create durable pricing distortions
- 04Behavioral biases can survive widespread awareness
- 05A factor may weaken if its sustaining mechanism disappears
How to run it
- 1
Find the counterparty
Describe which investors or institutions take the opposite side and why they continue doing so.
Pro tip Name a concrete incentive, mandate, risk preference, or bias rather than saying only that markets are inefficient.
Watch out A return premium cannot be owned by everyone simultaneously.
- 2
Test the risk rationale
Determine whether the factor suffers predictably in bad economic states and compensates investors willing to bear those losses.
Pro tip Study drawdowns in the regimes where the proposed risk should matter most.
Watch out Compensated risk still produces real, potentially prolonged losses.
- 3
Test structural impediments
Look for regulations, investment policies, leverage restrictions, benchmarks, or return targets that create persistent demand imbalances.
Pro tip Identify the exact policy that prevents the apparent arbitrage.
Watch out The premium may shrink if the constraint is relaxed or removed.
- 4
Test behavioral persistence
Identify recurring biases that make investors systematically overpay, underreact, or abandon positions at poor times.
Pro tip Prefer biases observed across markets and long periods.
Watch out Labeling unexplained residual returns as behavioral is not a substitute for evidence.
- 5
State the durability condition
Record why the mechanism should persist and what observable change would invalidate that belief.
Pro tip Turn the invalidation condition into a periodic monitoring item.
Watch out Do not assume that a historically durable mechanism is permanent.
In the wild
Many value companies have fixed physical capital that is difficult to alter during a recession. They can underperform sharply in late-cycle conditions, but investors able to tolerate that cyclical pain may receive a long-term premium as those firms benefit from operating leverage in recoveries.
→ Value is understood as compensation for bearing an identifiable economic risk rather than as a free return.
Some institutions have high return targets but cannot freely use leverage or change their mandates. They gravitate toward high-risk stocks and underweight low-risk stocks, creating a structural basis for minimum-volatility strategies.
→ The anomaly has an identifiable institutional counterparty and a condition under which it could weaken.
Common mistakes
Assuming discovery destroys every premium
Public knowledge does not remove a factor when investors still face risks, constraints, or biases that keep them on the other side.
Calling every anomaly behavioral
A behavioral explanation must identify a specific recurring bias and evidence that it affects prices.
Ignoring mechanism decay
Structural factors can weaken if regulations, mandates, or investment technologies change.
Is it for you?
Best for
It is best for investors evaluating whether a documented return premium has a durable economic foundation.
Not ideal for
It is not sufficient by itself to validate data quality, portfolio construction, costs, or investability.
From the transcript
“there are three. There's a reward for bearing risk, a structural impediment, and investors behavioral biases.”
“If you can't stomach that under performance, then well values not for you, but for those who can bear those risks of short term to…”
“Now, if that structural impediment disappeared and suddenly all of those institutions had much more flexible investment policies than perhaps we might see minimum volatility…”
From the episode
Andrew Ang Discusses Asset Management (Podcast)
Andrew Ang