Some of the most consequential 8-K events come from companies few datasets cover
Event data for equities often starts with the big indexes. That is where the trading volume is, so it is where coverage is deepest. It is also where some of the most consequential 8-K events are rarest.
How rare is rare?
Across every 8-K filed from January 2022 to August 2026:
| Event (8-K item) | Filings | Companies | Arrives with a press release |
|---|---|---|---|
| Delisting notice or listing-rule failure (3.01) | 8,799 | 2,976 | 34% |
| Change of auditor (4.01) | 3,915 | 2,419 | 9% |
| Past financial statements can no longer be relied on (4.02) | 1,044 | 801 | 17% |
| Earnings results (2.02), for comparison | 82,924 | 5,404 | 98% |
2,976 different companies filed a delisting notice. That is about twice the number of companies in the S&P Composite 1500, so at least half of them sit outside it: these are mostly small-company events.
Why does the press-release column matter?
Almost every earnings filing comes with a press release, so the market hears the news on the newswire first. Most auditor changes, restatement warnings and delisting notices do not: for them, the 8-K is often the first public word. Research on these filings finds abnormal trading around both the event and the filing, with some item types drifting in the expected direction for weeks afterward; non-reliance disclosures (4.02) have averaged about −2% over the following 20 days.
The point: the 8-Ks where the filing itself is the news are concentrated in companies outside the big indexes. Covering them means covering every filer.
- Lerman and Livnat, "The new Form 8-K disclosures", Review of Accounting Studies (2010): abstract.
- "Stock Price Reactions to Item 4.02 Disclosures in SEC Form 8-K Filings", 2007 to 2023: study.