Performance measurement tools

1. Performance Metrics vs Engagement Metrics (Gamification Achievement Systems Tips)
2. Challenges vs Quests (Player-Centric Gamification Tips)
3. Earnings vs Revenue (Virtual Economy Gamification Tips)
4. Rewards vs Incentives (Player-Centric Gamification Tips)
5. Information Ratio Gotchas (Hidden Dangers)
6. Player Ratings vs Player Rankings (Gamification Player Progression Tips)
7. Kelly Criterion Vs Sharpe Ratio (Clarified)
8. Leaderboards Vs. Progress Bars: Productivity Boosters (Explained)