NFL 2021 Week 21 (Conference Championships) Predictions – Zoltar Agrees with Vegas but I Do Not

Zoltar is my NFL football prediction computer program. It uses custom reinforcement learning and a neural network. Here are Zoltar’s predictions for week #21 (conference championships) of the 2021 season. It usually takes Zoltar about four weeks to hit his stride and takes humans about eight weeks to get up to speed, so weeks six through nine are usually Zoltar’s sweet spot. After week nine, injuries start having a big effect.

Zoltar:      chiefs  by    6  dog =     bengals    Vegas:      chiefs  by    7
Zoltar:        rams  by    6  dog = fortyniners    Vegas:        rams  by  3.5

Zoltar theoretically suggests betting when the Vegas line is “significantly” different from Zoltar’s prediction. In mid-season I usually use 3.0 points difference but for the first few weeks and last few weeks of the season I go a bit more conservative and use 4.0 points difference as the advice threshold criterion. In middle weeks I sometimes go ultra-aggressive and use a 1.0-point threshold.

Note: Because of Zoltar’s initialization (all teams regress to an average power rating) and other algorithms, Zoltar is much too strongly biased towards Vegas underdogs. I need to fix this.

For week #21 (division championships) Zoltar’s predicted margins of victory are close to the Vegas point spreads so Zoltar recommends no wagers. As a human being who watched games all season long, I would bet on the Vegas favorite Chiefs over the Bengals. My human brain says that the Chiefs will crush the Bengals and easily win by more than the 7.0 point spread.

A bet on the favorite Chiefs will pay off only if the Chiefs win by more than the point spread of 7.0 points (in other words by 8 points or more). If the Chiefs win by less than 7.0 points or if the Bengals win by any score, the wager on the Chiefs is lost. If the Chiefs win by exactly 7 points, the wager is a push.

Theoretically, if you must bet $110 to win $100 (typical in Vegas) then you’ll make money if you predict at 53% accuracy or better. But realistically, you need to predict at 60% accuracy or better.

In week #20, against the Vegas point spread, Zoltar went 1-0 (using the standard conservative 4.0 points as the advice threshold), correctly liking the favorite Chiefs over the Bills. Overall, for the season, Zoltar is 66-53 against the spread (~55%).

Just for fun, I track how well Zoltar does when just trying to predict just which team will win a game. This isn’t useful except for parlay betting. In week #20, just predicting the winning team, Zoltar went 1-3 which is bad.

In week #20, just predicting the winning team, Vegas — “the wisdom of the crowd” also went 1-3, the same as Zoltar.

Zoltar sometimes predicts a 0-point margin of victory, which means the two teams are evenly matched. There are no such games in week #21. In those situations, to pick a winner (only so I can track raw number of correct predictions) in the first few weeks of the season, Zoltar picks the home team to win. After that, Zoltar uses his algorithms to pick a winner.


Left: My prediction system is named after the Zoltar fortune teller machine you can find in arcades.

Center: A British “Blind Man Fortune Teller” machine from the 1920s. Predictions include the bizarre “Beware of the window”, and the interesting “Go, get thee a wife. She’ll mind thy folly”. A second coin slot is for charitable donations to the National Institute for the Blind.

Right: The “Columbian” fortune teller machine (1892) is a combination fortune teller and primitive slot machine. Fortunes include “Fortune will be thine by marriage” and “Rum is your worst enemy”.


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