Any time you try to measure income from trading you will have a problem because of survivorship bias. At any given time there will be some average of what current traders are making, but that will be skewed to the upside because the winners hang around and the losers drop out. So whatever mean (or median) income you find will actually be much lower. If we assume that the statistic of 90% of traders failing is true, then it would probably be safe to say that both the median and mean incomes are negative for trading.
That's not to discourage anyone from trading if that is their passion, just a reality check. Seems like a lot of people hear something like (totally hypothetical, I don't know the actual number) "well the average trader makes $100k per year" or whatever and then the newbie says "well, I've always been better than average" and thus makes the assumption that the average figure will be an easy accomplishment. In actuality, its the average income of the 10% that have survived. And to top that off, the average is a constantly moving number as changes in market condidtions can help even the worst traders or hurt even the best.