Quote from melo:
Numbers are what brings your fund up on the screen initially. Audited returns required to back them up. Run comparisons with peer group and other metrics to rank the candidates. That's the 20%.
Qualitative is the major element - Third-party checks/investigation on the principals' backgrounds, a long phone interview to hear the manager articulate his strategy and risk management systems, follow-up questions. If they stay on the shortlist, a visit to the fund's offices and meeting ALL the personnel. Ask friendly administrators/prime brokers etc. about the manager/fund.
Is the cycle favorable for the strategy is another consideration. There are obvious times when merger arbitrage, conv arb etc., is saturated, or economic cycles when distressed is likely benefit.
If you're marketing to intermediaries, you need to know what your target audience is likely to want for its clients, or if it's for institutions, what their constraints are. Institutions will also want to meet the manager in person.
Typically this due diligence process will take 2-3 months. And at the end of it, the ultimate qualitative test is your gut instinct. After a while in the business, as in many others, you begin to get a nose for when something doesn't stack up. Very bright hedge fund managers can be very bright at covering up and cooking up. Frauds are not easy to detect, and ultimately that's often a bigger risk than the fund blowing up since style drift is a little easier to pick up on the radar screen.
The above is necessarily a generalisation.