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Defensive Points per Game: Defense is Back Baby!

Week 8 Update

If you followed my blog last week, you would have read my analysis on Offensive Points per Game as it relates to Wins. My analysis last week which included data through the first seven weeks of the college football season, discovered that both Offensive & Defensive Points Per game had just about the same Predictive strength for determining wins. However after re running my predictive analysis model this morning to include statistics through week 8 (October 21, 2018), it turns out that Defensive Points per Game is now a stronger predictor of Wins than Offensive Points per Game.

My cumulative week 8 predictive analysis shows that Defensive Points Per Game as a key driver for wins has a predictive strength of 52% while Offensive Points Per Game as a key driver of wins has a predictive strength of 42%. So in simple terms, through week 8 scoring defense has more of an effect on Wins than scoring offense.

Predicitive Strength

A reminder on PS: You can use predictive strength to compare the predictors. Predictive strength is displayed as a percentage. A predictor with a predictive strength of 100% perfectly predicts a target. A predictor can be a single input or a combination of inputs. So the closer to 100% the stronger of a predictor it is, hence Defensive Points per Game being a stronger predictor of wins than Offensive PPG through 8 weeks of the season.

Our Analysis on Defensive Points per Game

As always, here at Ace Football Analytics we want to know if there is a statistically significant main effect on Wins. In this case, is there a significant, strong main effect of Defensive Points Per game on Wins? We set out to answer this question with the following:

1) To reject the Null Hypothesis (Fancy Statistics Term) that the Win means (averages) are equal across the categories of Defensive Pts. Per game. In simple terms we are setting out to see if in fact Defensive points per game leads to more wins.

2) Once we confirm that Defensive Pts. Per game is a strong predictor of wins, we want to identify the number or range of Defensive points per game that positively impact the number of wins. As you will soon see, the difference of a couple points per game in either direction can be the difference between winning and losing, or in the case of a college football coach, the difference between sitting home watching bowl games from the couch or participating in a bowl from the sidelines.

For this analysis, since Wins are a continuous target, a linear regression (ANOVA) based approach is used. This approach uses several techniques to assess the linear relationship between the input of Defensive Pts. per Game & the continuous target of Wins. As you can see from the graph below, there is a statistically significant, strong main effect of Defensive Pts. per Game on Wins. The important term here is Significant. When a result is statistically significant, we mean that it is unlikely that the result occurs because of chance or random fluctuation. Since statistical significance was achieved, we can say that the lower the Defensive points per game the higher likelihood of winning. We can confidently reject the hypothesis that Wins are equal across all categories of Defensive Points per Game. This is easily identifiable by the graph as you follow from left to right. The further to the right is a higher average of Defensive Points per Game which leads to a lower average win total for that group. You can see the linear relationship between the two by the line getting lower as it travels further to the right. In simple terms, the more points you give up, the less wins you average.

Again, you shouldn’t need an advanced degree in statistics to come to that conclusion, but what should comfort our coaches out there is that you don’t need to be the 1985 Chicago Bears or need to pitch shutouts each week in order to have a chance at winning.

Average win Totals by Defensive PPG

Below is our analysis on the defensive point totals so far this year and the average number of wins associated with each group. Each bar represents the Wins Average at a level of defensive points per game. Each group contains 26 teams for a total of all 130 FBS teams.

20.2 Def PPG is the Magic Number

You can see that the magic number for defensive points per game is less than 20.2 points per game. The teams that have held opponents to this level of scoring are averaging just about 6 wins each.

33.4 Def PPG is the Kiss of Death

Compare that to the teams in the bottom group who are giving up a total of more than 33.4 points per game. Those teams giving up more than 33.4 PPG are averaging only 2.2 wins each. Below is a picture of the teams who fall into the High and Low category of Def PPG along with their win totals.

The Middle Groups:

The middle groups consists of 3 categories. The Group with the second Highest win average is the group that holds opponent between 20.20 – 24.0 PPG with an average of 4.8 wins per team followed by the group that holds opponents between 24.0 – 28.0 PPG with an average of 3.8 wins per team. The 3rd of the middle group are teams that hold opponents between 28.4 – 33.4, these 26 teams average 3.1 wins each. This is really my favorite part of the analysis because it shows how just a few points more or less can be the difference between winning and losing. So wich category does your team fall into? This info should give your team a target to strive for in the second half of the season in order to improve your win total.

Want More Info?

Be sure to subscribe in order to get weekly updates, as our analysis changes based on updated data. I’m curious to see how both the offensive and defensive predictive models change as the season progresses. I am always happy to answer questions, provide additional information or even help you analyze games. Feel free to contact me through the website with a request. I also offer my data collection excel file for a small fee which contains thousands of sortable data on all 130 FBS teams. I am available for self /opponent scouting, game analysis or general questions, so please reach out by email. You can purchase my weekly data source file through the store tab or by emailing me directly. I promise you that you can’t find a file like this anywhere. I have done all the work, with thousands of data points for each 130 FBS teams in an easy to sort excel file. I update this file each week, making it easy for you to do your own analysis.

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