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Debunked: The bye week creates an unfair advantage

Here’s a mid-season Wednesday Way-Back.

Way back in July Poseur wrote a column to address the caterwauling that the Bama fans have done over the horrible injustice of having to play teams coming off a bye. We know the general story here…Alabama does not lose football games to other teams. Sometimes they un-win, sometimes they beat themselves, and sometimes they get caught in the travesty of playing a team that had a bye the previous week. So, Poseur wrote a column to undercut that idea. His column and the data he provided got me thinking about the issue a bit more.

Poseur’s analysis is a good start to examining the purported advantage of the bye week. As with most statistical analyses, there are multiple ways of examining the question, and, so there are ways to challenge the hypothesis with more rigor.

Poseur compiled SEC records for each team after a bye week, both over the last 10 years, and since expansion in 1992. He looked at the cumulative records for all teams, saw that it is approximately 50%, and concluded there is no great advantage. Had there been, say, a 65% winning percentage, he should have concluded otherwise.

A more pointed question would be to compare each team’s winning % after a bye vs. that team’s win % in games not after a bye. So, I found each team’s SEC record since 1992 and over the last 10 seasons (I stopped at 2012 since we’re only partially through this season). Then I subtracted Poseur’s numbers to get the non-bye week data. Finally, I did a z-test for each team’s win% to see if there is any statistically significant difference between win% after a bye and win% on a non-bye week. In these tables, z= the z statistic. The greater the absolute value of this number, the greater the effect of the bye week. If z is negative, it means a team has a lower win % after bye week than it does after a non-bye week. If z is positive, the team has a greater win% after a bye week. In these tables p = the p-value, which is a measure of confidence in the statistical test and the metric by which statisticians accept or reject a hypothesis. Conventionally, if p≤0.05 we reject the null hypothesis (that there is no difference). So, where p ≤0.05, the bye week has a statistically significant effect.

since 1992

team

win%, all

win% after bye

win% non-bye

z

p

Alabama

0.653

0.708

0.641

0.6635

0.255

Arkansas

0.468

0.269

0.497

-1.9971

0.023

Auburn

0.587

0.545

0.587

-0.4080

0.341

Florida

0.775

0.852

0.762

1.0151

0.156

Georgia

0.627

0.654

0.619

0.3166

0.375

Kentucky

0.268

0.364

0.253

1.2147

0.113

LSU

0.606

0.571

0.610

-0.4089

0.341

Ole Miss

0.375

0.375

0.375

0.0000

0.500

Miss. St

0.364

0.500

0.331

1.4687

0.072

S. Carolina

0.429

0.500

0.416

0.8822

0.187

Tennessee

0.633

0.636

0.629

0.0680

0.264

Vanderbilt

0.179

0.154

0.183

-0.3546

0.363

last10years

team

win%, all

win% after bye

win% non-bye

z

p

Alabama

0.655

0.700

0.649

0.3206

0.375

Arkansas

0.481

0.182

0.529

-2.1386

0.017

Auburn

0.610

0.500

0.622

-0.6700

0.251

Florida

0.699

0.889

0.676

1.3174

0.093

Georgia

0.667

0.800

0.629

1.2424

0.108

Kentucky

0.250

0.222

0.254

-0.2057

0.417

LSU

0.741

0.636

0.757

-0.8530

0.198

Ole Miss

0.325

0.091

0.362

-1.7843

0.038

Miss. St

0.300

0.385

0.284

0.7302

0.242

S. Carolina

0.506

0.875

0.466

2.1979

0.014

Tennessee

0.476

0.583

0.457

0.8066

0.209

Vanderbilt

0.250

0.286

0.247

0.2301

0.409

Not surprisingly in light of Poseur’s analysis, in the larger dataset (since 92) there is only 1 team with a statistically significant difference in performance post-bye week. That’s Arkansas, and they are worse after a bye. So, if you want to argue that a bye week is a benefit for a team, the data refute your point. But, they don’t just fail to support your point--the only case in which there is an effect, causal or coincidental, indicates the opposite of the Bama fan whine. If you look at a smaller, less statistically powerful data set (last 10 years) there are statistically significant differences for Arkansas, Ole Miss, and South Carolina, but only South Carolina has seen an advantage to playing after a bye week. It’s worth mentioning that MSU has done well after a bye week (see the since92 table), although the difference still fails statistical significance.

This analysis is not without limitations, of course. I’m not considering if the opponent is also on a bye week (but then the hypothesis is limited to the effect on a team coming off the bye). No consideration of home/away/neutral field is made. No adjustment for quality of opponent is made…maybe you would see a more profound difference if you only looked at games vs. ranked teams. And the teams that stand out--Arkansas, MSU, and USC—might shed some light on this. Does Arkansas typically play better opponents coming off their bye? Has USC have a tendency to play Kentucky after a bye week? Or, if you want to dig deeper you could examine other metrics to test this hypothesis. For example you could test if the bye week has an effect on scoring margin, turnovers, or number of penalties. But in terms of winning, the data have spoken…a bye doesn’t help an SEC team win a conference game.

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