Certainly you need a lot of samples for +/-. I would think 20 games would be enough but maybe not. I overstated its value - lots of things go into a player's value which can be hard to quantify. Kind of like hitting behind a runner to move him from second to third with no outs. I was watching the FSU game and Maddox cut to the basket and stopped. Aluma led him with a pass that bounced out of bounds without being close to anyone. Who gets that turnover? If a player consistently ends up with +/- that exceeds his team mates, then it very well mean something.