Form 13F: Institutional Holdings

Institutional investment managers exercising discretion over more than $100 million in specified US-listed securities must file quarterly. The report lists each position: the security, the number of shares and the market value at quarter end.

The threshold catches a very wide population: hedge funds, mutual fund managers, pension funds, banks, insurers and family offices. That breadth is what makes the aggregate useful even though any individual filing is limited.

• It is 45 days late. A position shown may have been sold weeks before the filing appeared.
• It is long-only. A manager fully hedged with shorts or puts appears as an outright long holder.
• It excludes non-US listings, bonds, cash and most derivatives, so it is a partial view of a portfolio.
• It shows no cost basis, so there is no way to know what was paid.
• It shows no conviction. A position can be a hedge, a client-directed holding, or an index sleeve.
• Confidential treatment can be requested, so a position being accumulated may be omitted entirely and disclosed later.

The second is the one that most often inverts a reading. A fund that appears to hold a large long position may be running a market-neutral book in which that holding is one leg of a pair, and nothing in the filing distinguishes the two.

Aggregated across every filer, it is a real measure of institutional ownership: what proportion of a company's shares sit with reporting managers, whether that proportion is rising or falling, and how concentrated it is.

Changes in aggregate ownership across a quarter are far more robust than any individual manager's position, because they are not sensitive to one filer's strategy or hedging. Errors in individual interpretation average out; the total does not.

A stock where institutional ownership is very high and rising has already been bought by the constituency that could buy it, which is a different situation from one where ownership is low. This is a structural observation about who holds the shares, not a view about the company.

It connects directly to correlationCorrelationHow closely two holdings move together, which decides whether they diversify anything.Read the full explanation. Holdings crowded with the same institutions tend to be sold together when those institutions reduce risk, which is why a portfolio of names that look unrelated by sector can behave as one position in a drawdownDrawdownThe decline from a peak to the following trough, in percent.Read the full explanation.

The obligation applies to institutional investment managers exercising discretion over one hundred million dollars or more in Section 13(f) securities, which is a specific published list of US-listed equities and some options. Everything about that sentence limits what the aggregate data can describe.

• A large fund trading only futures, currencies or foreign listings files nothing at all.
• Positions may be omitted under a confidential treatment request, granted where disclosure would reveal an ongoing acquisition programme.
• Holdings are reported at the manager level, so a firm with several strategies produces one combined list.
• Short positions are entirely absent, which means a hedged book is reported as though it were long only.

Amendments matter too: a 13F-HR/A can add positions previously withheld under confidential treatment, sometimes months later. A position appearing in an amendment was held at the original date and was not disclosed then.

Most commentary on 13F data reports changes: a manager added, trimmed or exited. Each of those descriptions rests on assumptions the filing does not support, and several ordinary explanations produce the same reported change.

The pro rata explanation in the second row accounts for a large share of reported activity at multi-strategy firms and is almost never mentioned. A fund that grew twenty percent through inflows will report every position as increased by roughly twenty percent, having made no decision about any of them.