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Wade Geraci
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​A Statistical Analysis of College Quarterbacks’ Potential

04/24/2014 12:36am
Replayed from 2014 NFL Draft
Adam Ondo

There are four quarterbacks projected to go in the first round in this year’s draft. They are Texas A&M’s Johnny Manziel, Central Florida’s Blake Bortles, Fresno State’s Derek Carr, and Louisville’s Teddy Bridgewater. Two of the debates that analysts have been promoting with regards to these four quarterbacks are whether or not height or passing attempts in college are factors that will influence how they play in the NFL. I’ve compiled a dataset of retired and current NFL quarterbacks in order to run regressions testing the usefulness of these factors as predictors of NFL success. 

Bortles is 6’5’’, while Manziel is only 6’0’’, so the height of quarterbacks has been thrust back into the spotlight in recent months. This was discussed extensively two years ago when the 5’11’’ Russell Wilson was drafted by the Seattle Seahawks in the third round of the draft. New York Jets quarterback Michael Vick’s 6’0’’ frame has also come under scrutiny, as he has seen scores of his passes swatted down by linemen and linebackers. Some analysts have also speculated that Derek Carr will be more successful than other top quarterback prospects because he has attempted 1630 passes in college, while Manziel has only attempted 863 passes and Bortles 891. The findings of this study don’t lend any support to these claims. For the purposes of this study, a dataset of quarterbacks, and their career stats in both college and the NFL, was compiled. The quarterbacks sampled were all drafted in the 21st century, meaning that they were selected in one of the last 14 drafts, starting with the 2000 draft. In order to be included in the study, the quarterbacks needed to have started at least 16 games or attempted at least 400 passes in the NFL. This yielded 73 usable observations. 

The first test examined the relationship between height and NFL completion percentage. The model was: NFLCP = H + CCP + NGS, where NFLCP is NFL completion percentage, H is height, CCP is college completion percentage, and GS is NFL games started. Height didn’t have a statistically significant effect on NFL completion percentage. That being said, there may have been some selection bias. In other words, if short quarterbacks were not very talented on average, then they would not have been included in the study as they would not have been given the opportunity to start 16 games or attempt 400 passes. 

The second test used the following model to examine the effects of college pass attempts on NFL quarterback rating: QBR = CPA + CCP + CYA, where QBR is NFL quarterback rating, CPA is college pass attempts, CCP is college completion percentage, and CYA is college yards per attempt. College pass attempts did not have a significant effect on QBR, but college completion percentage had a positive effect with a magnitude of .536 that was statistically significant at the 0.1 level. In other words, if college quarterback “A” has an accuracy of 58 percent and college quarterback “B” has an accuracy of 64 percent, then we would expect quarterback “B” to have a professional QBR that is three points higher than that of quarterback “A”. 

One might assume that the reason accurate college passers have higher QBRs in the NFL is because accuracy in college translates over to the NFL. However, a third test investigating the relationship between NFL completion percentage and college completion percentage did not yield statistically significant results or show a statistical correlation. This does not mean that there is no correlation; it just means that one cannot be proved using this specific dataset. However, there may be a confounding variable that was not controlled for in the study. The likely candidates would be the lack of interceptions thrown by accurate college passers or the propensity for those passers to make larger gains on the passes they do complete. 

The results of the study were inconclusive with regards to height and college pass attempts, but the completion percentage finding is interesting. These factors are just a couple that should be looked at when judging a quarterback, but it may make sense to give a little more weight to Manziel’s 68.9 completion percentage, especially since Bortles’ is four percent lower.

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