Methodology
The Enhanced Defensive Index (EDI) is a Bayesian framework designed to evaluate individual defensive impact across five distinct dimensions.
The 5 Dimensions of Defense
D1: Shot Suppression
Measures a defender's ability to lower their opponent's field goal percentage compared to their expected percentage.
- Adjusted for Matchup Difficulty (defending stars vs. role players).
- Uses Bayesian shrinkage to handle small sample sizes.
D2: Shot Profile
Evaluates the types of shots a defender forces. Elite defenders force opponents into inefficient mid-range shots rather than layups or corner 3s.
- Rewards rim protection (low FG% at rim).
- Rewards perimeter defense (limiting 3PT attempts).
D3: Hustle Index
Quantifies defensive activity that doesn't always show up in the box score.
- Components: Deflections, Charges Drawn, Contested Shots.
- Weighted by position and minutes played.
D4: Defensive IQ
A ratio-based metric assessing defensive playmaking relative to mistakes.
- Formula: (Steals + Blocks) / (Fouls + 1).
- Identifies disciplined defenders who create turnovers without fouling.
D5: Anchor / Rebounding
Measures the ability to end defensive possessions.
- Primary metric: Defensive Rebound Percentage (DREB%).
- Role-adjusted: Heavily weighted for Bigs, less for Guards.
Efficiency Model
EDI introduces an "Efficiency" coefficient to balance volume and effectiveness.
Input (Effort)
Weighted average of Hustle (D3) and IQ (D4).
Output (Impact)
Weighted average of Suppression (D1) and Profile (D2).
Efficiency Ratio
Actual Output / Expected Output (based on league-wide regression).
*For partial seasons, efficiency is stabilized using Bayesian shrinkage (K=10) to prevent small-sample outliers.
Validation Results
EDI was validated against official NBA defensive metrics across 5 seasons (2019-2024), measuring how well each metric identifies actual All-Defensive Team selections.
All-Defensive Team Coverage
Players correctly identified in each metric's top rankings (out of 50 All-Defense selections)
| Metric | Top 10 | Top 20 | Top 30 |
|---|---|---|---|
EDIOurs | 19/50 | 25/50 | 32/50 |
| DEF_RATINGNBA Official | 9/50 | 16/50 | 23/50 |
| DEF_WSNBA Official | 11/50 | 24/50 | 29/50 |
Superior Coverage
EDI identifies 32 out of 50 All-Defensive Team players in the Top 30 rankings, outperforming DEF_RATING (23/50) and DEF_WS (29/50). This demonstrates that the multi-dimensional approach captures defensive value that single-number metrics miss.