Thursday, December 31, 2015

2015 Early Season Power Rankings - The Results

In which we rank the rankings...

Power rankings are everywhere, but how do we know if they are any good? If they are intended to be predictive, we can test them for their predictive value. So, for the past three years, I have archived a cross section of power rankings from early in the NFL season (after week four). Then, once the season is done, I assess each ranking's accuracy in predicting future wins in that same season.

Each team's win percentage for weeks 5-16 (week 17 excluded) is rank ordered. This is then tested for agreement with each power ranking. I use the Spearman Rank Correlation coefficient for this purpose. A Spearman value of 100% would indicate perfect agreement between two rankings (e.g. if 1-32 in win percentage lined up identically with the power ranking in question). A value of -100% would indicate complete disagreement between the two lists, meaning 1-32 in win percentage lines up with 32-1 in the power ranking. A value of 0% would mean, roughly, no correlation between the two rankings.

I archived the week 4 power rankings in this post from October. As a reminder, the rankings I evaluate are: Football Outsiders DVOA, ESPN's FPI (as a replacement for Brian Burke's AFA efficiency rankings), the Simple Ranking System, ESPN's official NFL power rankings, FiveThiryEight's Elo rankings, and the Betting Market Rankings published here at inpredictable.

Sunday, December 27, 2015

The Colts are alive, but play a virtually meaningless game today

Owing to a strange confluence of tiebreaker scenarios, the Colts' game today against the Dolphins has virtually no impact on its playoff chances. According to my simulations, the Colts make the playoffs in 6.7% of the simulations in which they win, and in 6.1% of the simulations in which they lose., a swing of just 0.6%.

Contrast that to the impact the Texans-Titans game has on the Colts' playoff odds: The Colts make the playoffs in 18.7% of the simulations in which the Texans lose, and just 0.2% of the simulations in which the Texans win.

Saturday, December 26, 2015

NFL Playoff Implications Week 16

Here are the playoff implications for the NFL's week 16 games. The purpose of this feature is to highlight games that have a significant impact on the playoff picture (see this post for background).

The playoff implications below are derived from a 50,000 round simulation of the remainder of the NFL season. I use my daily NFL rankings to simulate future games. I can group the simulation runs by the outcome of each game and then see how a team's playoff chances vary between the two groups. The interactive table at the bottom of the post will allow you to see corresponding results for any game or team. The results of the three Thanksgiving games have already been taken into account in the tables below.

Ranking Week 16 Games by Leverage

The table below ranks the week 16 games by total leverage. Leverage in this context is a measure of both how uncertain a game's outcome is (games between evenly matched teams have higher leverage) and how much the playoff picture swings as a result of that outcome.

Turnover Index Week 16

Here are the Turnover Index picks and results for week 16. The Turnover Index is a simple betting strategy based on the theory that the market overvalues defensive turnovers when judging team strength. See here and here for more background.

Of our two picks from week 15, one pushed and the other lost. But due to bet size, the net effect on bankroll amounted to a rounding error (for the second week in a row).

Here are the season to date results:

weekbetswonstarting
bankroll
amount betprofitsending
bankroll
6 1 1 $1,000 $40 (4.1%) $37 $1,037
7 3 1 $1,037 $79 (7.7%) ($29) $1,008
9 2 1 $1,008 $66 (6.6%) ($51) $956
10 3 1 $956 $43 (4.6%) $3 $959
11 1 1 $959 $11 (1.2%) $10 $970
12 3 2 $970 $45 (4.7%) ($34) $935
13 1 1 $935 $13 (1.4%) $12 $948
14 1 1 $948 $0 (0.1%) $0 $948
15 2 0.5 $948 $12 (1.3%) ($0) $948


Thursday, December 24, 2015

In the AFC, Strength of Victory Could Determine the Postseason

Professional sports tiebreaking procedures tend to be an exercise in multiple redundancy. In the NFL, to break a tie within a division, there are 12 potential steps, starting with head to head record, progressing through divisional and conference records, strength of schedule metrics, various scoring margin measures, and ultimately culminating in step 12, a coin flip.

In a previous analysis, I found that this tiebreaking system was sufficiently redundant. Based on 10,000 simulations of the 2013 season, I found that there was just a 0.01% chance of the 8th tiebreaker, net points scored and allowed, needed to break a tie. That left a 3 tiebreaker buffer before the last resort coin flip was needed.

With just two weeks remaining in the 2015 regular season, we are still in no danger of a coin flip determining the postseason participants. However, there does appear to be a good chance that both the AFC North and AFC South will need one of the more esoteric tiebreakers to determine their respective division winners.

Saturday, December 19, 2015

NFL Playoff Implications Week 15

Here are the playoff implications for the NFL's week 15 games. The purpose of this feature is to highlight games that have a significant impact on the playoff picture (see this post for background).

The playoff implications below are derived from a 50,000 round simulation of the remainder of the NFL season. I use my daily NFL rankings to simulate future games. I can group the simulation runs by the outcome of each game and then see how a team's playoff chances vary between the two groups. The interactive table at the bottom of the post will allow you to see corresponding results for any game or team. The results of the three Thanksgiving games have already been taken into account in the tables below.

Ranking Week 15 Games by Leverage

The table below ranks the week 15 games by total leverage. Leverage in this context is a measure of both how uncertain a game's outcome is (games between evenly matched teams have higher leverage) and how much the playoff picture swings as a result of that outcome.

Turnover Index Week 15

Here are the Turnover Index picks and results for week 15. The Turnover Index is a simple betting strategy based on the theory that the market overvalues defensive turnovers when judging team strength. See here and here for more background.

Our sole pick from week 14 was successful. However, the edge was so small that the Kelly Criterion dictated that we bet just 0.1% of our bankroll, so the impact on overall results was negligible.

Here are the season to date results:

weekbetswonstarting
bankroll
amount betprofitsending
bankroll
6 1 1 $1,000 $40 (4.1%) $37 $1,037
7 3 1 $1,037 $79 (7.7%) ($29) $1,008
9 2 1 $1,008 $66 (6.6%) ($51) $956
10 3 1 $956 $43 (4.6%) $3 $959
11 1 1 $959 $11 (1.2%) $10 $970
12 3 2 $970 $45 (4.7%) ($34) $935
13 1 1 $935 $13 (1.4%) $12 $948
14 1 1 $948 $0 (0.1%) $0 $948


Sunday, December 13, 2015

NFL Playoff Implications Week 14

Here are the playoff implications for the NFL's week 14 games. The purpose of this feature is to highlight games that have a significant impact on the playoff picture (see this post for background).

The playoff implications below are derived from a 50,000 round simulation of the remainder of the NFL season. I use my daily NFL rankings to simulate future games. I can group the simulation runs by the outcome of each game and then see how a team's playoff chances vary between the two groups. The interactive table at the bottom of the post will allow you to see corresponding results for any game or team. The results of the three Thanksgiving games have already been taken into account in the tables below.

Ranking Week 14 Games by Leverage

The table below ranks the week 14 games by total leverage. Leverage in this context is a measure of both how uncertain a game's outcome is (games between evenly matched teams have higher leverage) and how much the playoff picture swings as a result of that outcome.

Saturday, December 12, 2015

Stephen Curry is No Stat-Padder

Stephen Curry close up.jpg It's been kind of under the radar, but Stephen Curry is having quite the season. He leads the league in a variety of box score stats, both traditional and advanced. He is #1 in points per game, field goals made, and three pointers made (the latter by a ridiculous margin). He also leads the league in PER (34.0), True Shooting Percentage (0.692), Win Shares (6.3), Box Plus/Minus (12.7) and Real Plus Minus (10.90).

As defenders play him tighter near the three point line, he simply extends the topology of the court, knocking down 26, 28, 30 foot shots with better accuracy than DeAndre Jordan makes free throws.

Another stat in which Curry is dominant is Win Probability Added (WPA), which I publish here on my site. Win Probability Added, as I've defined it, takes all field goal attempts, free throw attempts, and turnovers for each player, and weights them according to the impact those plays had on team win probability. This is the "anti-stat padder" stat, as it effectively ignores performance during garbage time. And with the Warriors playing the way they are this season, garbage time cometh, and that right soon. This stat also places much more emphasis on clutch shooting, with higher rewards for a made clutch shot, and stiffer penalties for a miss.

Turnover Index Week 14

Here are the Turnover Index picks and results for week 14. The Turnover Index is a simple betting strategy based on the theory that the market overvalues defensive turnovers when judging team strength. See here and here for more background.

Our sole week 13 pick was successful, with the Saints covering in a wild game against the Panthers.

Here are the season to date results:

weekbetswonstarting
bankroll
amount betprofitsending
bankroll
6 1 1 $1,000 $40 (4.1%) $37 $1,037
7 3 1 $1,037 $79 (7.7%) ($29) $1,008
9 2 1 $1,008 $66 (6.6%) ($51) $956
10 3 1 $956 $43 (4.6%) $3 $959
11 1 1 $959 $11 (1.2%) $10 $970
12 3 2 $970 $45 (4.7%) ($34) $935
13 1 1 $935 $13 (1.4%) $12 $948


Sunday, December 6, 2015

NFL Playoff Implications Week 13

Here are the playoff implications for the NFL's week 13 games. The purpose of this feature is to highlight games that have a significant impact on the playoff picture (see this post for background).

The playoff implications below are derived from a 50,000 round simulation of the remainder of the NFL season. I use my daily NFL rankings to simulate future games. I can group the simulation runs by the outcome of each game and then see how a team's playoff chances vary between the two groups. The interactive table at the bottom of the post will allow you to see corresponding results for any game or team. The results of the three Thanksgiving games have already been taken into account in the tables below.

Ranking Week 13 Games by Leverage

The table below ranks the week 13 games by total leverage. Leverage in this context is a measure of both how uncertain a game's outcome is (games between evenly matched teams have higher leverage) and how much the playoff picture swings as a result of that outcome.

Saturday, December 5, 2015

Turnover Index Week 13

Here are the Turnover Index picks and results for week 13. The Turnover Index is a simple betting strategy based on the theory that the market overvalues defensive turnovers when judging team strength. See here and here for more background.

The good news is that our week 12 picks went 2-1 against the spread. The bad news is we lost the wrong bet. The betting strategy dictated we bet a combined 0.7% of our bankroll on the two winning bets. But we had 4.1% bet on the Cowboys to cover against the Panthers on Thanksgiving.

In what was practically a single game refutation of the Turnover Index, the Panthers, who led the league in defensive turnovers, refused to regress to the mean. Instead, they continued their greedy ways, picking off Tony Romo three times, two of which were returned for touchdowns.