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Towards a unified understanding of relative age effects
Nick Wattie a; Stephen Cobley a; Joseph Baker ab
a
Carnegie Faculty of Sport and Education, Leeds Metropolitan University, Leeds, UK b School of Kinesiology
and Health Science, York University, Toronto, Ontario, Canada
First Published:November2008
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Journal of Sports Sciences, November 2008; 26(13): 1403–1409
Towards a unified understanding of relative age effects
NICK WATTIE1, STEPHEN COBLEY1, & JOSEPH BAKER1,2
1
Carnegie Faculty of Sport and Education, Leeds Metropolitan University, Leeds, UK and 2School of Kinesiology and
Health Science, York University, Toronto, Ontario, Canada
Downloaded By: [Wattie, Nick] At: 17:31 2 November 2008
(Accepted 16 May 2008)
Abstract
When athletes are placed into annual age groups to organize and coordinate sport participation, certain (dis)advantages
occur as a result of the subtle age differences within these groups. These differences, termed ‘‘relative age effects’’, have been
consistently related to youth and adult sport attainment. However, there has been a lack of consistency in the terminology
used in this area of research. In this paper, we consider the operational terms used in relative age research, discuss
appropriate applications of terminology, and suggest directions for future research. Importantly, we argue for a unified
understanding of what ‘‘relative age’’ means, stressing the need for clarity in directing future advances in the field.
Keywords: Sport, youth, relative age, development, constituent year effect
Introduction
The term ‘‘relative age’’ has traditionally been used
to refer to the subtle age differences between those in
the same annual age group (Barnsley, Thompson, &
Barnsley, 1985). Since correlations between educational attainment and school pupils’ relative age were
first reported (Armstrong, 1966; Freyman, 1965), a
substantive amount of research in the domains of
education and sport (for a review, see Musch &
Grondin, 2001) has sought to replicate these patterns
and explain their occurrence. However, as research
in this area has progressed, there has been a clear lack
of consistency in the operational terms used and, in
some cases, misapplication of the underlying framework. As research continues to progress, there is a
need to establish clear and consistent definitions to
avoid confusion with other existing research frameworks. To this end, the objectives in this paper are to
consider operational terms in relative age research,
clarify appropriate applications of terminology, and
suggest directions for future research.
An overview of relative age research in sport
Common practice in sport settings has been to group
children and youth according to chronological age,
as a way to ensure that each child can learn
developmentally appropriate skills and is able to
compete in an environment of equal footing in
relation to his or her peers. Typically, this has led to
the use of annual age-grouping systems, whereby a
selection date is used to group children into agespecific cohorts. For example, using a selection date
criterion of 1 September, children eligible to play
‘‘Under 7s football’’ in England must be more than 6
but less than 7 years old between 1 September and
31 August of that playing season. The result is that
those born immediately after the selection date
criteria are approximately 12 months older than
their team-mates born just before the end of agegrouping dates. Traditionally, such variations in age
within an annual age group have been referred to as
relative age differences, and their consequences
referred to as ‘‘relative age effects’’ (Barnsley et al.,
1985; Musch & Grondin, 2001).
Relatively older children within an annual age
group are more likely to be selected for school sports
teams (Cobley, Abraham & Baker, 2008; Wilson,
1999) and competitive youth sports teams (Barnsley
& Thompson, 1988). These inequalities, which
provide an advantage to relatively older players,
persist into adolescent levels of play and subsequently into elite and professional competition
(Barnsley et al., 1985; Grondin, Deschaies & Nault,
1984). Although soccer and ice hockey have been the
Correspondence: N. Wattie, Carnegie Faculty of Sport and Education, Leeds Metropolitan University, Fairfax Hall, Beckett Park Campus, Headingley, Leeds
LS6 3QS, UK. E-mail: [email protected]
ISSN 0264-0414 print/ISSN 1466-447X online Ó 2008 Taylor & Francis
DOI: 10.1080/02640410802233034
Downloaded By: [Wattie, Nick] At: 17:31 2 November 2008
1404
N. Wattie et al.
most extensively studied sports (for a review, see
Musch & Grondin, 2001), relative age effects have
also been observed in several other sports, including
tennis (Dudink, 1994), baseball (Thompson, Barnsley, & Stebelsky, 1991), cricket (Edwards, 1994),
netball (O’Donogue, Edgar, & McLaughlin, 2004),
and volleyball (Grondin et al., 1984).
In explaining relative age effects, it has typically
been suggested that relatively older children are
advantaged due to greater physical and psychosocial
maturity as well as increased experience of sport. A
leading hypothesis explains that greater maturation is
equated either with ‘‘talent’’ or with performance,
and as a result relatively older participants are more
likely to be favourably appraised compared with their
peers. This results in relatively older players being
selected to higher calibre teams, where they may
receive better coaching and competition, helping to
perpetuate their advantage over relatively younger
players.
While annual age groupings create relative age
differences and the associated maturational differences in the first place, they are not sufficient to
create relative age effects in sport. The cultural
popularity and importance of a sport influences the
existence of relative age effects via the number of
people wishing to play that sport (Musch & Grondin,
2001; Wattie, Baker, Cobley, & Montelpare, 2007;
Wattie, Cobley et al., 2007). If the number of people
wishing to participate grossly exceeds the infrastructure available (i.e. available teams, leagues, playingspace), more competition exists for participation.
Relative age effect-causing conditions become
further exacerbated in the contexts of sporting
structures that emphasize the values of winning and
the need to identify and develop ‘‘talent’’ at a young
age for the elite stage. Increased participation,
coupled with sport selection programmes, appears
to perpetuate relative age effects. Such a position is
supported by consistent findings in soccer, the most
popular sport globally, and ice hockey, the most
popular sport in Canada.
In summary, relative age research examines the
immediate and prolonged influence of a social
construct (i.e. annual age grouping) in sport and
education. However, within the relative age literature
there are inconsistencies in the use of operational
terms used to describe attainment inequalities. As
summarized below, these inconsistencies constrain
and complicate advances in research in this area.
The need for consistent and appropriate
operational terminology
Although the current discussion has exclusively used
the terms ‘‘relative age’’ and ‘‘relative age effects’’,
other terms such as ‘‘season of birth effect’’ (Edgar &
O’Donoghue, 2004, 2005; Stanaway & Hines, 1995;
Verhulst, 1992), ‘‘season of birth bias’’ (O’Donoghue et al., 2004; Simmons & Paull, 2001), and birth
date effect (Baker & Logan, 2007; Dudink, 1994;
Wilson, 1999) have also been used. However, using
such terms interchangeably may be confusing and
misleading. Using the term ‘‘season of birth’’ as
opposed to ‘‘relative age’’ is problematic because it is
associated with a separate area of research, with a
different theoretical framework. Originating during
the late 1920s (Barry & Barry, 1961), season of birth
research examines the influence of different prenatal
and perinatal seasonal environmental factors upon
human development. For example, season of birth
research hypothesizes that sunlight (i.e. vitamin D),
temperature, and/or viral exposure during gestation
are related to a number of health outcomes (Martin,
Foels, Clanton, & Moon, 2004; Torrey, Miller,
Rawlings, & Yolken, 1997). Over 250 studies from
over 30 countries have been published on ‘‘season of
birth’’ as a risk factor for developing schizophrenia
and other cognitive disorders (for reviews, see
Castrogiovanni, Iapichino, Pacchierotti, & Pieraccini, 1998; Torrey et al., 1997). This line of research
has also correlated season of birth with seasonal
affective disorder (Levitan et al., 2006), as well as the
risk of developing obesity in later life (Hillman &
Conway, 1975; Phillips & Young, 2000; Wattie,
Ardern, & Baker, 2008).
The assertion here is not that season of birth
research is without merit, but that care should be
taken when applying the two terms to avoid
misunderstanding the unique theoretical frameworks
of season of birth and relative age research. This
point should not be taken lightly, as mechanisms
from the ‘‘season of birth’’ framework (e.g. temperature and sunlight exposure during gestation) have
previously been presented as alternative explanations
for the occurrence of relative age effects (Martin
et al., 2004; Musch & Grondin, 2001). Furthermore,
use of the phrase ‘‘season of birth’’, when actually
referring to ‘‘relative age’’, contradicts a critical
element of relative age research: the central importance is a person’s age relative to that of their peers
within the same annual age group, a characteristic
dependent on time of birth relative to the selection
date used to place a child in a specific age group; not
the time of birth relative to a seasonal climatic cycle.
In fact, some of the most convincing research
supporting the traditional relative age framework has
shown that relative age effects exist independent of
specific months or ‘‘seasons’’ of the year. For
example, Musch and Hay (1999) observed that
soccer participation within Germany and Brazil,
countries using the same selection date criterion (1
August), demonstrated identical relative age effects.
That these countries had identical relative age
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Understanding relative age effects
effects, but are located in different hemispheres with
opposing climatic seasonal cycles, strongly suggests
that relative age and not seasonal conditions were
responsible for attainment inequalities. Similarly,
researchers have reported that when selection date
criteria have been changed, relative age effects shift
to reflect advantages for those born shortly after (i.e.
first three months) the new selection dates (e.g.
Helsen, Starkes, & Van Winckel, 2000; Musch &
Hay, 1999). Barnsley and colleagues (Barnsley &
Thompson, 1988; Barnsley et al., 1985) also debated
the validity of seasonal explanations in ice hockey,
pointing out that if seasonal factors were responsible,
then those born in December would be similarly
advantaged to those born in January, since the two
months share nearly identical seasonal conditions.
However, consistent attainment inequalities have
been observed between relatively older players born
in January and relatively younger players born in
December (Montelpare, Scott, & Pelino, 1998;
Wattie, Baker et al., 2007).
Although the use of alternative terminologies has
been the most prevalent inconsistency in the relative
age literature, a recent study by Medic and colleagues (Medic, Starkes, & Young (2007) stresses the
need to discuss the different ways that the term
‘‘relative age’’ has been used. In Masters competitions, athletes are typically grouped into five-year
age-bands (e.g. 40–44, 45–49 years). Subsequently,
the authors applied the term ‘‘relative age’’ to
describe an athlete’s age and year of participation
within an age-band. For example, in the 45–49 ageband, those 45 years of age, and therefore in their
first year of participation for that age-band, would be
described as being relatively younger (as defined by
Medic et al., 2007). Similarly, a 49-year-old would
be in their fifth year of participation within the ageband, and would be regarded as being relatively
older. Medic and colleagues also referred to an
athlete’s year of participation within an age-band as a
‘‘constituent year’’ (i.e. constituent year 1, constituent year 2, etc.).
Although this study is of interest because it
contributes to our understanding of performance
maintenance, ageing, and expertise, it is equally
interesting because it constitutes a new development
in relative age research. With the exception of Medic
et al. (2007), all previous studies have applied the
term ‘‘relative age’’ to refer to age differences within
a given annual age group. However, the use of the
term ‘‘relative age’’ in this context may be problematic.
In the traditional relative age framework, inequalities result from relative age differences caused by
annual age grouping policies used in youth sport
(these mechanisms have been discussed previously).
Scientists concerned with the immediate effects of
1405
annual age grouping policies used in youth sport
have examined relative age effects in youth and
adolescent sport (where athletes are still grouped for
participation using annual age groups). Researchers
concerned with long-term effects have examined the
existence of relative age effects at elite adult
standards of play (where annual age grouping is no
longer used to group athletes for participation). In so
doing, they hope to determine what adult athletes’
relative ages would have been in the youth leagues of
their sport (Barnsley et al., 1985; Grondin &
Trudeau, 1991; Montelpare et al., 1998; Wattie,
Baker et al., 2007).
However, the framework used by Medic et al.
(2007) steps outside the aforementioned framework,
does not retrospectively ascribe relative age based on
annual age grouping policies of youth sport, and
instead defines relative age more broadly. This
distinction is important in terms of study design,
and because this discrepancy encompasses different
causal mechanisms. The inequalities observed
among Masters athletes are more likely to be
associated with age-related declines in performance.
Although researchers have indicated variations in the
rates of decline (e.g. Baker, Horton, Pearce, &
Deakin, 2007; Bortz & Bortz, 1996; Starkes, Weir,
Singh, Hodges, & Kerr, 1999), these studies
collectively indicate that performance declines with
advancing age after peak performance. Since Masters
sport typically involves competitors who are past the
age of peak performance (which differs by sport), it is
reasonable to suggest that those at the start of a fiveyear age-band can function better than those at the
end of the same age-band.
Most interestingly, perhaps, it is also possible that
participation rate discrepancies among Masters
athletes may be the result of self-selection processes
based on psychosocial factors related to perceptions
of success via peer-group comparison within an ageband. Comparatively, participation inequalities observed by traditional relative research result from
being selected (or not selected) by an external party
(i.e. the coach).
Another important difference between the traditional relative age framework and the new framework
relates to the dynamics of an athlete’s relative age.
According to Medic et al. (2007), an athlete’s relative
age (i.e. constituent year) will change from year to
year as they progress through an age-band. Comparatively, within the traditional framework, relative
age remains a stable characteristic throughout the
developmental stages of youth sport participation
(unless selection date criteria change).
It could be argued that these differences are merely
a reflection of the different participation structures of
youth and Masters sport, and therefore that a
demarcation between the two types of ‘‘relative
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1406
N. Wattie et al.
age’’ may not be necessary. However, youth ice
hockey in Canada utilizes annual age grouping and
two-year competition age-bands. Nonetheless, previous relative age research in youth sports with twoyear age-bands (i.e. with two constituent years) has
used the traditional framework (e.g. Barnsley &
Thompson, 1988; Wattie, Cobley et al., 2007).
To better understand why the traditional relative
age framework has been used in this context, let us
consider a group of athletes entering their first of two
years of play in an Under-14s (Over-12s) age-band
(see Figure 1). All the players that enter their first
year of participation in this age-band (i.e. constituent
year 1) are an annual age group defined by a
selection date (e.g. 31 December), and therefore
within a 12-month age range (i.e. a selection year).
The next playing season, the aforementioned group
progresses together upwardly into constituent year 2
(but still in the Under-14s age-band). Naturally,
when our hypothetical annual age group enters their
second constituent year, a new annual age group
becomes eligible to occupy the first constituent year
(Figure 1 also illustrates the different dynamics of the
two frameworks).
The previous example demonstrates that the
demarcation between youth and Masters sport may
not be enough to warrant using the same term to
describe different frameworks. It also shows that it is
possible for the two frameworks to be observed
simultaneously in the same context. Researchers
could examine outcomes between athletes of different ‘‘relative age’’ as defined by the traditional
relative age framework, and of different ‘‘relative
age’’ as Medic and colleagues (2007) have described
(i.e. athletes from different constituent years). While
potentially educating, all aspects of such a study
(methods, results, discussion) would be difficult to
describe, and comprehend. It has been previously
mentioned that an essential step towards eliminating
relative age effects should be to raise awareness of
relative age discrepancies (Musch & Grondin, 2001).
Having two applications for the term ‘‘relative age’’
could make this aim particularly challenging.
In and of itself, the term ‘‘relative age’’ may be too
vague and ambiguous to satisfy the demands of
scientific rigour. However, it will be increasingly
problematic to use the same terminology to describe
and compare outcomes of two entirely separate
frameworks of research In light of the aforementioned issues, the use of alternative terminologies
may be prudent in future research. One solution
would be to maintain the designation ‘‘relative age’’
for work using the traditional framework (i.e. a social
construct related to a selection date) and an
alternative term for the new area of research
suggested by Medic et al. (2007). For instance, the
use of the term ‘‘constituent year effect’’ would be an
appropriate and less confusing description of the
underlying premise related to this work. Although
this point may be contentious, alternative terminologies may reduce confusion and misinterpretation of
the findings elicited by the two frameworks.
Directions for future research
Although a substantial amount of research has been
carried out on relative age effects in sport,
numerous avenues exist for future research. Most
relative age research in sport has sought to simply
identify the existence (or non-existence) of relative
age effects in terms of who are selected for
participation at a particular level of skill. However,
many more possibilities exist and should be
considered.
Figure 1. Comparison of constituent-year effect dynamics and relative age effect dynamics in youth sports with a multi-year age band
structure.
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Understanding relative age effects
To be clear, not all relatively young members of an
annual age group experience failure as a result of the
relative age inequality. In fact, some relatively younger athletes are selected for competitive youth sports
teams and subsequently partake in elite competition
during adulthood. A recent study by Sherar and
colleagues (Sherar, Baxter-Jones, Faulkner, & Russell, 2007) found that although relative age effects
existed in competitive youth ice hockey, relatively
younger children who were selected did not differ in
physical size and stature from their relatively older
peers. These findings provide evidence that physical
characteristics such as an above-average stature may
increase the likelihood of being selected to competitive level teams and, perhaps more importantly, the
data imply a selection bias by coaches, where players
are selected on the basis of physical maturity and not
necessarily components of skill. While these data are
useful in suggesting something about the factors
underpinning the creation of relative age effects, the
measures examined have largely been gross proxies of
maturity such as total stature and weight. More
specific measures of physical (e.g. skeletal) maturity
have the potential to add considerable depth to our
understanding in this area.
Moreover, cognitive growth and maturity have
received little or no attention. Martin et al. (2004)
postulated that the development of certain parts of
the brain is strongly correlated with chronological
age, particularly in boys, who often do not reach full
frontal cortex maturity until late adolescence. Frontal cortex abilities such as controlling attention and
impulses, forming concepts, manipulating ideas,
engaging in behaviour when a goal is remote, and
control of gross motor activity are all important
factors for relative age-mediated academic performance (Martin et al., 2004). Although these functions have been described in relation to performance
in academic settings, and with regard to the
appropriateness of specializing in one sport at an
early age (Patel, Pratt, & Greydanus, 2002), such
functions could be important prerequisites for
complex tactical team sports, such as soccer and
ice hockey. In the future, therefore, relative age
researchers in sport may benefit from considering
such factors when assessing differences between
relatively older and younger athletes, particularly in
the early levels of sport participation. Perhaps such
chronologically related neurological and cognitive
capabilities may be related to coaches’ perceptions of
‘‘coachable’’ or ‘‘smart’’ players, as a result of an
athlete’s ability to conceptualize and learn offensive/
defensive strategies alongside technical skills. Such
research may be particularly helpful to coaches
interested in developing informed training programmes based on consideration of different players’
developmental abilities and needs.
1407
Although the majority of research has shown that
relatively older players have consistent advantages
over their relatively younger peers, recent research
suggests that relatively younger members of a cohort
may not be as disadvantaged as previously believed.
Recent work examining injury trends in youth ice
hockey found that relatively older players were more
likely to sustain injuries requiring hospital treatment
(Wattie, Cobley et al., 2007). Other preliminary data
suggest relatively younger professional athletes are
more sought after (Baker & Logan, 2007) and obtain
higher salaries (Ashworth & Heyndels, 2007).
Vaeyens and colleagues (Vaeyens, Philippaerts, &
Malina, 2005) observed that once selected to teams,
relatively older players had no advantage over their
relatively younger team-mates in terms of playing or
roster selections. In future, researchers may benefit
from considering other ways in which sport-specific
contexts influence relative age-associated outcomes.
It can no longer be assumed that relative age acts to
exclusively and uniformly advantage relatively older
athletes. For example, it is possible that relatively
older athletes also experience deleterious psychological outcomes associated with their relative age.
While relatively younger athletes may be more likely
to experience negative comparisons and low selfefficacy, relatively older athletes may experience
disproportionate pressure to perform well or unreasonable high expectations from coaches and
parents.
Researchers have also repeatedly promoted the
need to examine relative age effects in female sports
contexts (Musch & Grondin, 2001; Wattie, Baker
et al., 2007). The limited relative age research in
female sports suggests that gender plays an important
role in determining an athlete’s experience, progress,
and development in sport (Vincent & Glamser,
2006; Wattie, Baker et al., 2007). Further research
on the interactions between gender and relative age
may prove beneficial.
While numerous avenues for future research exist,
it could be argued that one of the most important
directions would be for researchers and practitioners
alike to work towards eliminating relative age effects.
To date, no research in sport has worked towards
this goal. Despite changes and/or modifications to
other aspect of sport (e.g. equipment, rules of play,
and coaching), relative age effects have persisted in
culturally popular sports for several decades. This
stresses the need for creative research aimed at
removing this participation and attainment inequality, and the challenge that researchers face in doing
so. Research-driven interventions and collaborations
with those interested in youth talent identification
programmes need to be conducted. If relative age
effects are to be eliminated, then the efficacy of
interventions and coach-education curriculum will
1408
N. Wattie et al.
need to be tested and determined. With these points
in mind, efforts of both theory-driven researchers
and applied sport psychologists will be of great value.
Conclusion
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To progress relative age research, scientists need to
be cognisant and clear in their operational definitions
and theoretical underpinnings. In this paper, we have
attempted to establish some clarity, but invite a more
thorough discussion of these issues. Another requirement is a proactive plan for future research in this
area. At the very least, relative age research must
move beyond studies that simply identify the effect in
another context. More meaningful information may
come from examinations where relative age effects
are expected but not found. In addition, continued
examination of the mechanisms driving these effects
and their possible solutions is needed.
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