Sample size in poker determines when results reflect skill versus variance. For online cash games, typically 100,000-200,000 hands are required for winrate within 1 BB/100 of a 95% confidence interval. For tournaments, higher variance demands even larger samples: 500-2,000 tournaments depending on format and ROI. Making decisions about stakes level, game change, or winrate identity based on small samples is one of the most common bankroll management errors. With insufficient samples, short-term negative results do not prove negative EV, and positive results do not confirm positive EV.