Stale Marks and Understated Volatility
Because private asset values are only updated a few times a year by the manager holding them, their reported returns look artificially smooth — understating true volatility and correlation with public markets in a way that can make private assets look safer than they really are.
Prerequisites: Valuation Marks and Fair Value Policy
A public stock's price moves every trading day, so a full year of daily returns captures every up and down swing. A private company held in a fund is typically revalued only once a quarter, and even then, the new mark is often influenced by the previous quarter's mark rather than reflecting a fully fresh, independent estimate each time. The result is a reported return series that looks far smoother than the underlying business's true economic ups and downs — a statistical artifact called stale pricing or return smoothing, not evidence that the asset is actually less risky.
Why smoothing distorts the numbers
If a manager's marks lag reality and get adjusted gradually rather than all at once, the reported quarterly returns end up correlated with each other over time (this quarter's return partly reflects information that should have shown up last quarter), which mechanically shrinks the measured standard deviation of returns even though the true underlying volatility of the business hasn't changed at all. The same lag also mutes the measured correlation between private assets and public markets — private equity often looks like it moves independently of stocks in a spreadsheet of quarterly returns, purely because its marks catch up to a market move a quarter or two late, not because the actual businesses are genuinely insulated from the same economic forces hitting public companies.
Why this matters beyond a statistics footnote
Investors and consultants who build portfolios using these reported (smoothed) numbers can end up systematically overestimating private equity's diversification benefit and underestimating its true risk, which can lead to larger-than-appropriate allocations to private assets in a portfolio built on the assumption that they behave less like stocks than they actually do. This same lag is a root cause of the denominator effect: when public markets fall sharply and quickly, private marks haven't caught up yet, so private holdings mechanically become a larger share of a portfolio's total value than they will look once those marks eventually adjust downward too.
A smooth-looking return series from a private fund is partly a measurement artifact of infrequent, lagged valuation updates, not proof the underlying assets are genuinely less volatile or less correlated with public markets than they truly are.
Don't read a low measured correlation between private equity and public equities in a historical dataset as a real diversification benefit you can rely on in a crisis. When public markets fall hard and fast, private marks typically follow with a lag of a quarter or two — the "diversification" often shows up as delay, not genuine independence.
Related concepts
Practice in interviews
Further reading
- Cliffwater / academic literature on smoothing bias in private-asset return series