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NFL Modeling Blog

Solving for the adjusted ELO and other model adjustments...

11/24/2020

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I am revealing that a pivotal component of my model is the ELO ratings assigned by FiveThirtyEight to each team every week. One can obtain .json's with their data from the website and take the ELO data from there. I have partially been using ELO to weight each game, but I have only been using the most recent ELO. For example, if a team had a great week but then a streak of horrible weeks, the great week would never even be accounted for. One of the changes I brought to the model was to time-weight the ELO ratings based on week played. 

To do this, I created a factor that I would use to adjust the weighting of the week, so that I would account for all of the preceding weeks, but they wouldn't all be weighted evenly. 

To solve for the ideal ELO factor to use, I floored the different teams' adjusted ELO values based on the hundreds value and aligned it with a sorted range of the teams' winning percentages. This, I believed, would grant me the highest accuracy with regards to finding a fair ELO value. 

They were matched as such:
x<=1300   0.000-0.200
x=1400     0.200-0.400
x=1500.    0.400-0.600
x=1600.    0.600-0.800
x>=1700.  0.800-1.000

The goal was to minimize the variance of the difference of the count between each subsection. 

Excel's Solver couldn't solve for this, so I decided to do so myself, and I found that there is an incredible amount of overall variability in the 0-10 range, but an increased ELO factor mellowed the distribution out a lot. The ideal value ended up being 30, as this matched the columns up the most accurately. 

Also, I have changed the adaptive spread measures. I had been solving for it wrong before and only accounting for a difference in the positive spread, which is dumb on my part. I want to minimize both sides of it, not just the positive side. I accounted for the absolute value of the spreads and used solver to minimize that and got more of a mixed distribution of results. 

I have plugged these new values into the model, and I am ready to see how they work this upcoming week! Maybe it will have a better understanding of how to predict the Winners of this week's games and their corresponding spreads. Wish me luck! 
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    If you'd like access to the model, just email me, I'd be happy to share :) 
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