Abstract. Stocks jointly held by hedge-fund-like 13F filers co-move beyond what their characteristics explain, and they fall harder in the worst market months. Both effects are statistically significant. Neither clears the promotion hurdle this site applies before a result is treated as tradable, so crowding is classified as a risk measure rather than a signal.
What was tested
The August 2007 “Quant Quake” showed that positions held in common across leveraged managers unwind together, so that one fund’s deleveraging becomes every co-holder’s drawdown (Khandani and Lo, 2011). The question is whether that channel is visible in advance in disclosed holdings, and whether what is visible is strong enough to trade. Form 13F is the quarterly Securities and Exchange Commission holdings filing. A stock’s crowding is the number of hedge-fund-like filers holding it, read only once the filing deadline has passed. The claims, the fund filter and the number of tests were fixed before any filing was retrieved, so the correction for multiple testing existed before the results did.
| Measure | Value |
|---|---|
| Form 13F panel | 53 quarters, 2013 through mid-2026 (2.9 GB) |
| Filers screened | 11,750 |
| Hedge-fund-like filers | 1,216 |
| Fund filter | fewer than 250 positions; name turnover above 25% a quarter |
| Point-in-time lag | 45 days (filing deadline) |
| Co-held pairs, matched on sector and size decile | 3,312 |
| Excess residual correlation, six standard factors removed | approximately +0.9 correlation points |
| Crowded minus uncrowded quintile, worst decile of market months since 2014 | −142 basis points per month |
| Crowded minus uncrowded quintile, all months | −33 basis points per month |
| Tests declared in the pre-registration | n = 2 |
| Promotion hurdle | raw t of about 5, after halving gross return and doubling costs |
What the data show
If many funds hold the same two stocks, those stocks should co-move beyond what sector, size and the standard factors explain (Anton and Polk, 2014). They do, against matched controls the crowd does not co-hold, and the effect is real but economically small. The stress result is the larger one, and the crowd pays a modest toll in ordinary months as well. That is what the deleveraging channel of 2007 predicts.
| Claim | Effect | NW t | Outcome |
|---|---|---|---|
| Co-held pairs co-move (3,312 pairs) | +0.9 corr pts | 4.09 | held, not promoted |
| Crowded underperform in stress (14 months) | −142 bps/mo | −3.90 | held, not promoted |
Why neither is promoted
Promotion requires a claim to survive a re-audit run with a margin of safety, at a threshold set in the spirit of the multiple-testing corrections of Harvey, Liu, and Zhu (2016). Neither t-statistic reaches it. The stress result also rests on the handful of months the pre-registration anticipated, and a small sample remains a small sample however well it agrees with the prior. The finding stands as pre-registered. Crowding is a risk measure, not a tradable signal: it tells a risk desk where liquidity is narrow, and a trading desk nothing about what to buy.
| Limitation | Consequence |
|---|---|
| Survivorship-biased panel (current constituents only) | crowding is counted among survivors; reported statistics are upper bounds |
| Pre-registration specified industry matching; the available data support sector matching | deviation recorded in code before results existed |
| Pre-registered crowding measure specified scaling by float market cap decile; the implementation used unscaled counts | a second deviation, not previously listed here; it tilts the crowded quintile toward mega-caps and is only partially absorbed by the FF5+Mom residualization |
| 13F filings disclose neither short positions nor swaps, and the fund filter (fewer than 250 positions, turnover above 25% a quarter) excludes dealer banks by construction | an exposure of the Archegos type is invisible; equity held on swap by multi-manager platforms, which appears if anywhere in the prime broker’s own filing, sits outside this measure entirely. The crowding measured here is a floor, not a ceiling |
References
- Anton, M., and Polk, C. (2014). Connected Stocks. Journal of Finance, 69(3), 1099–1127.
- Harvey, C. R., Liu, Y., and Zhu, H. (2016). …and the Cross-Section of Expected Returns. Review of Financial Studies, 29(1), 5–68.
- Khandani, A. E., and Lo, A. W. (2011). What Happened to the Quants in August 2007? Evidence from Factors and Transactions Data. Journal of Financial Markets, 14(1), 1–46.