On the surface, the Bears’ running game didn’t change much from 2016 to 2017.
- In 2016 they ran for 1,735 yards (17th in the NFL) and averaged 4.6 yards per carry (6th).
- In 2017 that shifted to 1,788 yards (16th) and 4.2 yards per carry (11th).
The total yards slightly increased, the yards per carry slightly decreased, but the overall run game stayed average to above average.
But sometimes total numbers don’t tell the whole story, and some fans felt like Chicago’s rushing attack took a step back in 2017 due to inconsistency. For every dominant game (222 yards and 2 TD against Pittsburgh, 231 yards and a TD against Baltimore) there was an absolute clunker (6 yards against Philadelphia, 20 yards against Tampa Bay). DBB reader Butch thought that this perceived inconsistency was particularly frustrating, and he asked me to look into it.
Quantifying inconsistency is actually fairly straightforward using standard deviation, which is a measure of how much variability exists in a set of numbers. Basically, the higher a standard deviation is, the more inconsistent the numbers in that sample are. To see where the Bears ranked, I looked at their rushing yardage and yards per carry for each game in 2017 and found the standard deviation for both sets; I also did the same thing for the other 31 teams in order to give some context to the Bears’ results.