Revisiting Mutual Fund Portfolio Disclosure

We document that CRSP and Thomson contain a large number of voluntarily reported mutual fund portfolios that are not in SEC filings while, additionally, CRSP and Thomson are missing a large number of SEC mandated portfolios available in SEC filings. Voluntary disclosure is likely motivated by convenience and advertising. While mandated portfolios are more window dressed, performance and disclosure costs are similar using Thomson or SEC data, validating prior findings using Thomson. CRSP, however, contains inaccurate position information prior to 2008. Our findings have important implications, such as highlighting a 35% increase in observed manager trading by combining data sources.