UC Irvine

We document that CRSP and Thomson contain many voluntarily reported mutual fund portfolios that are not in SEC filings while, additionally, CRSP and Thomson are missing many SEC mandated portfolios available in SEC filings. We document that the voluntary disclosures are likely driven by convenience rather than duplicity. Although mandated portfolios contain securities with more return momentum, we find use of SEC or Thomson data lead to similar empirical findings. 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.