Private equity firm Apollo Global Management (APO) has reported first-quarter earnings, with profit up 72% to $792. However, this is an industry full of volatility, and there's a lot to understand here before jumping in. Where should investors be looking? In this video, Fool financial analysts David Hanson and Matt Koppenheffer discuss some of the key metrics involved in understanding the private equity business and compare some of the biggest players in this space.