When I compare TC2000 v12.5 % Shares Held by Institutions to Nasdaq.com's Institutional Ownership I usually find that they are not the same. They are different by as much as 20 or 30 % sometimes. Is there a reason they are often different?

Who provides Worden the % Shares Held by Institutions data? I wonder if your data and Nasdaq's data is updated at different intervals. In any case, I would like to determine which one is more accurate because they are often not the same.