I've never seen any studies on crappie handling. As my colleague from Arkansas pointed out, there hasn't been much focus on the catch and release aspect. There are a few studies on the handling of largemouth bass that might apply. They concluded that for heavier fish, a two handed hold (one on the lower jaw, and one on the tail) shortened the time needed for the released fish to regain its equilibrium. However, they did not find a major difference in survival between a one handed (one on lower jaw) hold, vs a two handed. It would seem reasonable that the same principles would apply. Crappie do not get as heavy, but their jaw structures are also not as "beefy". The best practice is to keep the fish vertical instead of horizontal unless you are using the two handed hold. Dropping the fish in the water likely has a very minimal effect, however, if you're slinging them 20 feet in the air and judging their dives like the Olympics, then it may be doing some damage.

More important factors for survival are air exposure, livewell temp differences and O2, and excessive slime removal from mishandling (flopping around on carpet, etc.)