NBA Betting Against the Public 2003-05 Midseason Review

  • ARTICLE # 1 NBA – BETTING AGAINST THE PUBLIC STATS 10/31/2003 – 1/25/2005

This is the first in a series of articles that will examine the betting data found on Sports Insights. The goal is to evaluate past results and highlight inefficiencies in the sports betting marketplace. The first article tests the Win % of Sports Insights “Bet Against the Public” strategy.

NBA Bet Against the Public:

The following information is for educational and entertainment purposed only. The staff at SportsInsights.com has spent countless hours working to ensure all data used in our analysis is correct. The data used comes from our official archived info pages. We do not guarantee our data is error free although we’re tried our hardest to make sure every score and percentage is correct.

It is the core belief of SportsInsights.com that inefficiencies exist in the sports betting market. These inefficiencies are cause by the public’s psychological bias toward betting Favorites. Nobody likes betting on bad teams. It’s even harder for us to bet on horrible teams, but it is exactly this reason that produces a sizeable bias in the sports betting market. In the following series of articles, we demonstrate that inefficiencies exist in the sports betting market and we explain strategies for exploiting it.

It is impossible to predict the future. It is possible to use statistical analysis and risk modeling to test for inefficiencies in any marketplace. There is a fallacy that exists in sports betting. Sportsbooks DO NOT look to balance their action. Oddsmakers know that the public disproportionately bets Favorites. They factor this bias in when they create betting odds.  It is this public bias (betting favorites) that we look to measure.

We do not guarantee that the trends and biases we’ve found will continue to exist. Any serious academic research in the field of marketplace efficiencies realizes that over time these inefficiencies will disappear.  Once an inefficiency is discovered, it is only a matter of time until the market corrects itself. The following is a summary of our findings.

NBA Betting Against the Public: 10/31/03-1/25/05

Rules for Filtering Games:

  • Did not use data if it was 0% or 100%
  • NBA Data from 10/31/03 – 1/25/05 (1674 games)
  • Correct for 12/24/04 data error (entered twice)

We evaluate the “Bet Against the Public” strategy using the following criteria.

  • % bet threshold

The following tables look at Win % if a person bet on a team with X % (Public Bet %). Table 1 is based solely on Straight Bet %, Table 2 is based solely on Teaser Parlay Bet %, and Table 3 is based on the average between the two.

Table 1   NBA – Straight Bets

X % or Lower
(Public Bet %)
# Games Win % Avg Marg Win Avg Marg Loss  
50 1572 50.6 9.4 8.4
45 1240 51.9 9.4 8.6
40 903 50.5 9.4 8.7
35 611 51.1 9.2 8.2
30 369 53.1 9.6 8.4
25 207 50.7 8.8 7.9
23 152 55.3 8.9 8.3  
20 85 56.5 9.1 7.0
15 29 69.0 10.5 5.5
10 7 71.4 7.3 7.8

Table 2   NBA –Parlay/Teaser

X % or Lower
(Public Bet %)
# Games Win % Avg Marg Win Avg Marg Loss  
50 1604 50.9 9.6 8.2
45 1193 49.6 9.8 8.3
40 830 49.4 9.9 8.0
35 517 50.5 10.1 8.4
30 312 52.6 9.7 8.4
25 158 51.9 10.1 8.2
23 111 54.1 9.9 8.0
20 62 56.5 11.3 7.1
15 12 33.3 10.8 8.0

Table 3   NBA – AVG  Bets Straight &  Parlay/Teaser

X % or Lower
(Public Bet %)
# Games Win % Avg Marg Win Avg Marg Loss  
50 1617 50.9 9.5 8.3
45 1196 50.5 9.6 8.3
40 829 50.4 9.6 8.4
35 521 50.1 9.8 8.7
30 285 54.7 9.8 8.6  
25 135 54.8 9.4 8.9
20 41 58.5 8.2 6.3
15 9 77.8 6.8 7.5
10 2 100.0 5.3 -