Friday, June 13, 2014

Yards per carry and the NFL Draft

This post displays the potential importance of outliers.

Question Two:  How does the average of yards per carry for the first-choice running back differ from the average yards per carry for the second-choice running back?   How do the median, standard deviation, and skew of yards per carry for the first and second choice running backs differ?


Data:   The data used for this post can be found at



I originally collected the data at an NFL Web site.




Answer:

Information on career yards per carry for first-choice and second-choice running backs is displayed in the table below.

First-Choice Running Back
Second-Choice Running Back
Average of years per carry
3.91
3.99
Median of yards per carry
4.10
4.00
Standard deviation of yards
 per carry
0.80
0.25
Skew of yards per carry
-3.77
0.12



The average of yards per carry over the 33 draft years is slightly higher for second-choice running backs than for first-choice running backs.

The median of yards per carry is slightly larger for first-choice quarterbacks than for second choice quarterbacks.  

The standard deviation of yards per carry is over 3 times larger for first-choice running backs than for second-choice running backs.


The skew of first-choice running backs is highly negative indicating the existence of some very small observations.  The skew of the second-choice running back sample is 0.12 indicating the data is basically symmetrically distributed around the mean.

Discussion:


How can we explain these relatively strange results?    Larry Stegent the first-choice running back in 1970 blew out his knee in his first pre-season game.  He was included in our sample despite having zero yards.  He is an outlier.  Perhaps I should have excluded him from the sample. 


http://en.wikipedia.org/wiki/Larry_Stegent

Interested readers might want to compare the yards per carry statistics presented here to total career yards statistics discussed in a previous post.

http://dailymathproblem.blogspot.com/2014/06/running-back-career-yardage-statistics.html





#NFL Draft

#NFL

#outliers





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