Massive short positions.
Institution X buys 100 shares.
Hedge Fund Y borrows those shares from X for a fee, sells them short in the market to Institution Z.
Now both X and Z own those same 100 shares, although only Z has custody of them.
If you subtracted the short interest, the total would be 100% (or less, to the extent that ownership is unknown).
It’s a mistake, due to inconsistencies in the data. That can happen when different institutions report their holdings at slightly different times (so there’s overlap in reported transactions) or when there are large short transactions against a stock, resulting in multiple people reporting ownership of shares.
In short: institutional ownership reports are a bit sketchy and can be inconsistent.
It’s possible they have not netted out short sales. So if there are 100 shares outstanding, and I borrow 37 shares from you and sell them to Cecil Adams,the total long positions will be 137 shares or 137% of shares outstanding.
This page
reports large positions as a percentage of float. Float is not the total number of shares outstanding. It subtracts out shares held by long-term inside investors who are not likely to sell.
Scroll down here, and you will see that short interest is 19 million shares, total shares o/s is 38 million. So the short interest is 50% of the market cap. So if they had all the ownership information, it would total 150%.