Test-Retest Reliability (aka
Whose hands grew the most over the past month?)
The Senior Bowl, Shrine Game, and Collegiate Bowl all have
weighins which measure height, weight, arm length, and hand size. 80 players* got measured at one of these events, and then got measured again at the Combine (so far - DL, LB, and DB still to come). That creates a perfect opportunity to measure test-retest reliability - how consistent are the two sets of measurements with each other?
QB Brandon Allen, for example, weighed in at 6'1.5", 221 lb. at the Senior Bowl, with 30.5" arms and 8.5" hands. At the Combine, he weighed in at 6'1", 217 lb., with 31.25" arms and 8.875" hands. He lost 0.5" of height and 4 pounds, and gained 0.75" of arm length and 0.375" of hand size. (Though note that only Combine heights that I have are rounded to the nearest inch, so he may have lost as little as 0.125" of height.) How typical are those results? Did Allen get an unusually large increase in hand (and arm?) size from
his work with a masseuse?
On average, the 80 players lost 0.07" of height, gained 0.40 lbs., and gained 0.40" of arm length and 0.27" of hand size. So the growth of Allen's hands was far from unique - it was actually fairly close to the typical result.
Those numbers are just the average change - some players had an increase in hand size, some had a decrease. We can find the typical size of the change by taking the standard deviation of the change in hand size, and comparing it to the standard deviation of the players' hand sizes as measured at the Combine. Players' weights by 0.09 standard deviations, height by 0.13 standard deviations (though that is inflated by rounding), arm length by 0.31 standard deviations, and hand size by 0.55 standard deviations. Another way to put it: the correlation between the Senior Bowl (etc.) measure and the Combine measure is 0.996 for weight, 0.99 for height, 0.94 for arm length, and 0.85 for hand size. (Though some of the reason why weight seems so stable is that there is such a wide variation in weight - gaining or losing a few pounds doesn't make much of a dent in the weight gap between offensive linemen and wide receivers.)
In other words, knowing a player's Senior Bowl weight gives you a pretty precise estimate of what he'll weigh at the combine (compared to the overall variation in player weights). Knowing his Senior Bowl hand size gives you a fuzzier guess at what his combine hand size measurement will be (compared to the overall variation in player hand size). Though it is still pretty informative (e.g., psychologists are reasonably happy if their scales have a test-retest correlation over 0.70, and hand size had a 0.85 correlation).
Now that we have both sets of measurements, is our best guess of a player's actual size his combine measurement, which are standardized and (hopefully) done more carefully and professionally? Or should we take some sort of (weighted?) average of the two measurements?
Back to the title question: "Whose hands grew the most over the past month?" Unfortunately, the answer is that there is an 8-way tie, with 8 players' hands "growing" by a full inch. If we look at combined hand & arm growth, then the Stretch Armstrong award is shared by 2 RBs, Kenneth Dixon and Kenyan Drake, who each had 1" of arm growth and 1" of hand growth.
A spreadsheet with all 80 players' measurement changes is
here. Here are the biggest growers and shrinkers:
Height
+0.75" Devon Cajuste WO Stanford
+0.625" Malcolm Mitchell WO Georgia
+0.5" Jacoby Brissett QB North Carolina State
+0.5" Brandon Wilds RB South Carolina
+0.5" Joe Thuney OL North Carolina State
-0.625" Willie Beavers OL Western Michigan
-0.625" Le'Raven Clark OL Texas Tech
-0.625" Stephane Nembot OL Colorado
-0.625" Brandon Shell OL South Carolina
-0.625" John Theus OL Georgia
-0.75" John Lunsford PK Liberty
-0.875" Fahn Cooper OL Mississippi
Weight
+10 lb. Alex Lewis OL Nebraska
+8 lb. Parker Ehinger OL Cincinnati
+8 lb. Alonzo Russell WO Toledo
+7 lb. Joel Stave QB Wisconsin
+7 lb. Beau Sandland TE Montana State
+7 lb. Trevone Boykin QB TCU
+6 lb. Drew Kaser PK Texas A&M
-6 lb. Leonte Carroo WO Rutgers
-6 lb. Darrell Greene OL San Diego State
-6 lb. Dominique Robertson OL West Georgia
-9 lb. Ryan Malleck TE Virginia Tech
-9 lb. Jordan Payton WO UCLA
-10 lb. Vadal Alexander OL LSU
Arms
+1.125" Kyle Murphy OL Stanford
+1.125" Tajae Sharpe WO Massachusetts
+1.125" Chris Moore WO Cincinnati
+1" Joel Stave QB Wisconsin
+1" Drew Kaser PK Texas A&M
+1" Jeff Driskel QB Louisiana Tech
+1" Nick Vannett TE Ohio State
+1" Cody Whitehair OL Kansas State
+1" Kenneth Dixon RB Louisiana Tech
+1" Kenyan Drake RB Alabama
+1" Sebastian Tretola OL Arkansas
+1" Spencer Drango OL Baylor
+1" Leonte Carroo WO Rutgers
+1" Vadal Alexander OL LSU
-0.375" Geronimo Allison WO Illinois
-0.5" Ben Braunecker TE Harvard
-0.625" Jacoby Brissett QB North Carolina State
-0.875" Vernon Adams QB Oregon
Hands
+1" Kenneth Dixon RB Louisiana Tech
+1" Kenyan Drake RB Alabama
+1" Dak Prescott QB Mississippi State
+1" Cody Kessler QB USC
+1" Graham Glasgow OL Michigan
+1" Jerell Adams TE South Carolina
+1" Christian Westerman OL Arizona State
+1" Ricardo Louis WO Auburn
+1" Le'Raven Clark OL Texas Tech
+0.875" Brandon Shell OL South Carolina
+0.75" Charone Peake WO Clemson
-0.25" Dan Vitale RB Northwestern
-0.25" Dominique Robertson OL West Georgia
-0.375" John Theus OL Georgia
* There were 82 players, but then I threw out Notre Dame WR Chris Brown and Marshall RB Devon Johnson. When I looked into their numbers more closely because the changes were implausibly large, I found that they had different Shrine Game measurements reported
here and
here.