Interesting article in today’s Journal about stock returns around activist filings. We took a look at 13D and 13D/A filings (beneficial ownership of more than 5% of a voting class of a company’s equity securities), often associated with activist investments. We confirmed that the announcement return is large and positive, and more so for the original filings (13D) than for amendments (13D/A). There is also a runup leading into the announcement, presumably contemporaneous with the acquisition of the shares. However it doesn’t show any actionable effect beyond the announcement period.