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Regression Alert: Week 6 - Footballguys

50% of the variation in yards per target is explained by a player's yards per reception. The other 50% is prime territory for regression to the mean.

Welcome to Regression Alert, your weekly guide to using regression to predict the future with uncanny accuracy.

For those who are new to the feature, here's the deal: every week, I dive into the topic of regression to the mean. Sometimes I'll explain what it really is, why you hear so much about it, and how you can harness its power for yourself. Sometimes I'll give some practical examples of regression at work.

In weeks where I'm giving practical examples, I will select a metric to focus on. I'll rank all players in the league according to that metric, and separate the top players into Group A and the bottom players into Group B. I will verify that the players in Group A have outscored the players in Group B to that point in the season. And then I will predict that, by the magic of regression, Group B will outscore Group A going forward.

Crucially, I don't get to pick my samples, (other than choosing which metric to focus on). If the metric I'm focusing on is yards per target, and Antonio Brown is one of the high outliers in yards per target, then Antonio Brown goes into Group A and may the fantasy gods show mercy on my predictions.

Most importantly, because predictions mean nothing without accountability, I track the results of my predictions over the course of the season and highlight when they prove correct and also when they prove incorrect. Here's a list of all my predictions from last year and how they fared.


THE SCORECARD

In Week 2, I laid out our guiding principles for Regression Alert. No specific prediction was made.

In Week 3, I discussed why yards per carry is the least useful statistic and predicted that the rushers with the lowest yard-per-carry average to that point would outrush the rushers with the highest yard-per-carry average going forward.

In Week 4, I explained why touchdowns follow yards, (but yards don't follow back), and predicted that the players with the fewest touchdowns per yard gained would outscore the players with the most touchdowns per yard gained going forward.

In Week 5, I talked about how preseason expectations still held as much predictive power as performance through four weeks. No specific prediction was made.

Statistic For Regression
Performance Before Prediction
Performance Since Prediction
Weeks Remaining
Yards per Carry
Group A had 24% more rushing yards per game
Group A has 3% more rushing yards per game
1
Yards:Touchdown Ratio
Group A had 28% more fantasy points per game
Group B has 32% more fantasy points per game
2

In our Yards Per Carry bet, Group A managed to edge back ahead on the back of a 15-carry, 219-yard day by Isaiah Crowell. Absent that performance, Group B would have once again averaged more yards per game and more yards per carry than Group A.

I don't mean to suggest that we just ignore that game, but it does highlight two important principals. First, this is why I like using larger samples. The smaller the group of players being compared, the fewer weeks the comparison spans, the more a single outlier event will dominate the comparison.

Secondly, the fact that it's Isaiah Crowell that's carrying Group A shows why I never cherry-pick who goes into which group. At the time I made the prediction, I figured having Isaiah Crowell in Group A would have lowered Group A's per-game averages, not raised it. Instead, he's outrushed everyone except for Ezekiel Elliott.

There's one more week to go on that prediction, and Group B merely has to out-rush Group A by about 5 yards per game to still pull it out.

Meanwhile, as far as our second prediction goes, touchdowns have indeed been following yards. Both Group A and Group B scored four touchdowns in ten receiver games, (not counting Odell Beckham Jr Jr.'s passing score for Group B).

One of those ten receiver games for Group B came from Brandin Cooks, though; Cooks left the contest with a concussion before recording a single target. Meaning the "low-touchdown" Group B receivers were once again reached the end zone at a higher rate than the "high-touchdown" Group A receivers. Two weeks left to go.

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