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Born at the wrong time: selection bias in the NHL draft.

Robert O Deaner1, Aaron Lowen, Stephen Cobley

  • 1Department of Psychology, Grand Valley State University, Allendale, Michigan, United States of America. deanerr@gvsu.edu

Plos One
|March 6, 2013
PubMed
Summary

Relative age effects (RAEs) in sports occur when older athletes get more opportunities. This study found that in National Hockey League drafts, younger players were drafted later and had fewer chances, indicating pervasive selection bias.

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Area of Science:

  • Sports Science
  • Developmental Psychology
  • Sociology of Sport

Background:

  • Relative age effects (RAEs) are well-documented in sports and education, where older individuals within an age cohort often have advantages.
  • The underlying causal mechanisms for RAEs, particularly selection bias, remain unclear.
  • Selection bias involves evaluators unfairly limiting opportunities for younger individuals based on their relative age rather than their actual ability.

Purpose of the Study:

  • To directly test the selection bias mechanism as a cause of RAEs.
  • To investigate if selection bias influences player selection in professional sports drafts.
  • To quantify the impact of relative age on opportunities and career progression in the National Hockey League (NHL).

Main Methods:

  • Analysis of National Hockey League (NHL) player draft data from 1980 to 2006.
  • Comparison of draft positions and career benchmarks (games played, points scored) based on players' birth quarters.
  • Statistical examination to identify disparities in opportunities for players born in different quarters.

Main Results:

  • Players born in the third and fourth quarters of the year were drafted over 40 slots later than their productivity justified, compared to those born in the first quarter.
  • Individuals born in later quarters were approximately twice as likely to achieve significant career milestones.
  • This selection bias in NHL drafts persisted and did not diminish over the study period, impacting opportunities for younger players.

Conclusions:

  • Selection bias based on relative age is a significant factor contributing to RAEs in professional sports.
  • The bias is evident even among professional decision-makers evaluating adult athletes.
  • This suggests that selection bias related to relative age may be widespread across various domains.