Player Selection Bias in National Football League Draftees

Abstract

Beyer, KS, Fukuda, DH, Redd, MJ, Stout, JR, and Hoffman, JR. Player selection bias in National Football League draftees. J Strength Cond Res 30(11): 2965-2971, 2016-Relative age effects (RAEs) have been studied as a potential factor associated with player selection bias in numerous sports. However, little research has examined the role of RAEs among National Football League (NFL) draftees. The purpose of the current study was to determine the existence of RAEs in NFL draftees from the last 10 NFL drafts. Draftee birth dates were collected and divided into calendar and scholastic quarters (SQ1-SQ4). To determine the presence of RAEs in specific subsets, NFL draftees were grouped according to round drafted, position, level of conference play, and age at the time of the draft. Significant χ tests (p ≤ 0.05) comparing observed birth-date distributions vs. the expected birth-date distribution from the general population were followed up by calculating the standardized residual for each quarter (z > ±2.0 indicating significance). Overall, no RAEs were seen when birth-date distribution was assessed using calendar quarters (p = 0.47), but more draftees were born in SQ2 (December-February) than expected (p < 0.01; z = +2.2). Significantly more draftees were born in SQ2 than expected for middle-round draftees (p = 0.01; z = +2.4), skill positions (p = 0.03; z = +2.3), Power Five college draftees (p < 0.01; z = +2.6), and early draftees (p < 0.01; z = +3.1). However, reverse RAEs were seen among late draftees, with fewer draftees being born in SQ2 (z = -3.6) and more being born in SQ4 (June-August; z = +2.6) than expected. In contrast to previous research, the current study observed significant RAEs in NFL draftees from the last 10 years. This player selection bias should be considered when evaluating long-term athlete development models in American football.

Relative Age Effects in Elite Olympic Weightlifters

“…Countries use different cut-off dates which should also be examined for their role in RAEs. As previous studies have shown, scholastic quarters may present differently than calendar quarters in competition (4,18). Some other confounding factors could be considered in future studies, including age at time of competition and differences between competition years.…”

“…For instance, Hurley et al (18) found that in division I collegiate soccer, United States athletes had RAEs present when categorized by scholastic calendars. Beyer et al (4) found that RAEs were also present in National Football League draftees when assessed by scholastic quarters but not by calendar quarters. However, from this, RAEs were only present in skill positions and not in size positions.…”

“…The observed date of birth distribution vs. the expected worldwide date of birth distribution were compared using multiple chi square (x 2 ) goodness of fit tests, following the methodologies of previous research on RAEs (4,5,(10)(11)(12)(13)(14)(15)17,18,(21)(22)(23)(24)27,28,30,31). This analysis was run on the sample as a whole, each gender combined across weight classes, each previously defined weight class, and for each gender combined across weight classes, but separated into medalists and nonmedalists.…”

“…Relative age effects have been shown to be present in numerous sports (2)(3)(4)(5)(6)8,(12)(13)(14)(15)(16)(17)(18)20,(23)(24)28,(30)(31). Most of the sports that have shown RAEs to be present are based on the scholastic calendar or another age cut-off date designed to create a fair level of competition among cohorts.…”

Epidemiology and Impact of Prior Musculoskeletal Injury and Orthopaedic Surgery on Draft Rank, Availability, and Short-term Performance in Major League Baseball: A Summary Analysis and Matched Cohort of 1890 Predraft Players

“…15,18,20 In the National Football League (NFL), the impact of predraft injuries and surgical procedures, including anterior cruciate ligament reconstruction, rotator cuff tears, and shoulder labral tears, has been reported extensively from the medical records of the treating physicians; the findings portend unfavorable career prognoses for those with a musculoskeletal injury history, including a lower likelihood of a successful draft and a greater likelihood of decreased performance. 1,2,9,13,17…”