Blair William & Co/Il

What a 13F is

Any institutional manager exercising discretion over more than $100 million in US-listed equities must file a Form 13F with the SEC within 45 days of each quarter end, listing what they held on the last day of that quarter. The threshold was set in 1975 and has never been raised, so the filer population now runs to several thousand.

The four things it does not tell you

• It is stale. A filing describes positions as of quarter end and can arrive 45 days later. A manager who sold everything in week one of the new quarter files the same document as one who held.
• Long US equities only. No short positions, no cash, no bonds, no commodities, no foreign listings. A fund that looks heavily long in a 13F may be hedged in instruments that never appear.
• Not the whole firm. Assets are reported by the entity with discretion, so one manager can file under several CIKs, and the figure here is what that entity reported.
• Confidential treatment exists. A manager can apply to delay disclosing a position while building it. Those holdings appear later, if at all.

Why the biggest filers are not the interesting ones

The largest managers by reported value are index providers — they hold nearly everything, in proportion to the indices they track, because clients asked them to. Reading their filings for conviction is a category error. The filings worth attention are concentrated ones, where a small number of positions make up most of the portfolio, since that reflects a decision rather than a mandate.

The share-of-portfolio column is the one to read for this. A position that is 15% of a fund says something; the same dollar amount at 0.2% of an index tracker does not.

Where this comes from

The SEC's own quarterly Form 13F structured data sets, parsed here rather than bought from a vendor. Holdings are identified in the filings by CUSIP, and the mapping from CUSIP to ticker is the awkward part — that identifier is licensed rather than public, so the mapping is resolved through OpenFIGI and built up over time. Around 95% of reported value currently sits on a resolved ticker; the rest shows its CUSIP.

The rest of the section is on the Markets overview — including insider transactions, which are the same idea at the individual level, and the correlation finder, where each ticker's page carries its institutional ownership.