Increase in income Income per capita has been increasing steadily in almost every country.[5] Many factors contribute to people having a higher income such as education,[6] globalisation and favorable political circumstances such as economic freedom and peace. Increase in income also tends to lead to people choosing to work less hours. Developed countries (defined as countries with a "developed economy") have higher incomes as opposed to developing countries tending to have lower incomes.
I think it’s funny how 1500 is the amount of extra income you mention because that’s what I’m shooting for! If I can make that much more each month to supplement my regular income, I will have almost all of my school debt payed off in one year! I’m really motivated. I use Mechanical Turk with Amazon to perform menial task and get a few extra bucks. I also use Varolo which is a fairly new idea. I really think it has potential. If you don’t mind me promoting it, here it goes.
Portfolio income can come from multiple sources – interest/bond coupons, stock dividends, financial strategies including derivatives and capital growth.  Each offers some cash flow and some also offer potential capital gain with some risk from liquidity and volatile prices.  In this low-yield environment, many investors rely too heavily on cash flows and to pursue this are venturing further into riskier areas than they’d normally consider.