I've been meaning to ask
@Papafox - you're using % of trades that are short as an important element in your daily analysis. Do you know how that number is arrived at?
I ask because my first thought is that every trade has a buyer and a seller. Nobody buys without somebody else selling, and nobody sells without somebody buying. The one thought I have is if trades are reported with the additional detail of whether either end of the trade is doing the opposite - sell-to-open, or buy-to-close. Traders doing either are what I would consider short sellers.
Thus my interpretation is that 64-68% trades by short sellers really means that 64-68% of trades involve somebody doing sell-to-open or buy-to-close on either end of the trade (or of course, both ends of the trade).
Presumably that's share weighted, so 64-68% is really the % of shares involved in trades in which either or both ends of the trade are sell-to-open or buy-to-close. This might also help understand how such a high fraction of daily volume comes from people in a short position, yet the total number of shares short rises modestly, but not a million+ a day.
The problem here is that if trades aren't reported with the additional detail of each end of the transaction, then I'm really wondering about how trustworthy that piece of data is.
And if trades DO include that additional piece of information, then it seems like somebody with the desire could in fact reconstruct the total number of shares short on a daily basis and update it daily. Heck - real time as each trade with whether each side is opening or closing the position gets posted. But this level of detail about short interest isn't available (that I know of).
Thanks!