Quote from logic_man:
The best place to find research on day trading or individual traders in general is cxoadvisory.com or SSRN.
I've seen research there showing that anywhere from 20% to 50% of day traders were profitable during the period being researched. Split the difference and it would seem that about 1 out of 3 individual traders is profitable. Almost every study seemed to conclude that trading is a skill, not just luck.
Another interesting tidbit that I found in that research is that the most profitable traders tend to trade either the least frequently per day or the most frequently. So, either you've got one killer set-up which prints money a couple times per day or you've built an automated set-up that casts a broad net over the market to pull in profits from a wide number of situations. It's when you have neither of those that you are in trouble. This makes complete sense to me from a strategic perspective, since both a "focused" strategy and a "wide net" strategy can work, but hybrids of the two seem very likely to fail.
I haven't seen anything that speaks to the persistence of those profits, though, but I would imagine that the longer the research period, the lower the percent profitable.
As for the sources of a profitable individual trader's profits, it's either hedgers or less skilled individual traders. Sure, once in a while you might pull a profit out of a trade where a hedge fund guy is your counterparty, but that's not typical. Most of the time you are taking cash from Joe Six-pack. If, in time, JSP becomes a better trader, he will take his profits from the next generation of Joe Six-pack. That's just how it goes.