How much of the volume comes from trades done based on technical analysis? I would assume it is really hard to get any data on this, but I would be happy to hear about any studies or even educated guesses. I am mostly interested in the stock market, but also glad to hear about forex or commodities if this information is available there.
One reason why I am asking is that I started to wonder why most technical trading books, blogs, etc. describe the market as something only affected by information becoming available to people and psychological factors, resulting in patterns or signals that can be detected by indicators. Rarely do I hear people talking about patterns resulting from people doing technical trading, or trading systems based on assumptions of which other trading systems people are using. For example if enough people are trading according to some indicator, it would be possible to develop a system exploiting this. Why is this not so common? Is it because technical trading is so rare that it has no impact on the stock price, or is it because so many different systems are used that it averages out or becomes random noise, or is there some other reason?
I appreciate all help. Especially any volume breakdown information.