Download Height at age 18 years is a strong predictor of

Published by Oxford University Press on behalf of the International Epidemiological Association
Ó The Author 2006; all rights reserved. Advance Access publication 30 January 2006
International Journal of Epidemiology 2006;35:658–663
doi:10.1093/ije/dyl011
LIFE COURSE EPIDEMIOLOGY
Height at age 18 years is a strong predictor
of attained education later in life: cohort
study of over 950 000 Swedish men
Patrik K E Magnusson,1,3 Finn Rasmussen2* and Ulf B Gyllensten1
Accepted
10 January 2006
Background Adult body height has been related to socioeconomic position in cross-sectional
studies. Intelligence, shared family factors, and non-familial circumstances may
contribute to associations between height and attained education, but their
relative importance has been difficult to resolve.
Methods
A nation-wide record-linkage cohort study of over 950 000 Swedish men born
1950–75 followed with respect to attained education for up to 27 years after
measurement of height at age 18 (baseline). The association between height
and attained education in later life was investigated by logistic regression
modelling with adjustment for age, geography, parental socioeconomic position,
and cognitive ability. Shared family factors were accounted for in analyses of
full-brother-pairs using conditional logistic regression.
Results
The odds ratio (OR) for attaining higher education 7–27 years after baseline was
1.10 [95% confidence interval (95% CI) 1.09–1.10] in fully adjusted models
per 5 cm increase in height. Men taller than 194 cm were two to three times more
likely to obtain a higher education as compared with men shorter than 165 cm.
The association remained within brother-pairs, OR 1.08 (95% CI 1.07–1.10),
suggesting that non-familial factors contribute to the association between height
and education attainment. A significant interaction (P , 0.0001) was found
between year of birth, height, and attained education, showing slightly weaker
associations among later birth cohorts.
Conclusions The strong positive association between height and educational achievement
remaining after adjustment for year of birth, parental socioeconomic position,
other shared family factors, and cognitive ability may reflect educational discrimination based on height although residual confounding cannot be ruled out.
Keywords
Adult height, education, intelligence, socioeconomic factors, heritability,
discrimination
Introduction
1
2
3
Department of Genetics and Pathology, Rudbeck laboratory, Uppsala
University, Sweden.
Department of Public Health Sciences, Karolinska Institute, Stockholm,
Sweden.
Present address: Department of Medical Epidemiology and Biostatistics,
Karolinska Institute, Stockholm, Sweden.
* Corresponding author. Child and Adolescent Public Health Epidemiology
Group, Department of Public Health Sciences, Karolinska Institute,
Norrbacka, SE-17176 Stockholm, Sweden. E-mail: [email protected]
Body height in early adulthood is influenced by both genetic and
environmental factors acting during prenatal growth, childhood,
and puberty. Since a long time, socioeconomic factors have
been known to be related to adult body height.1–4 Starvation
and infectious diseases influence growth, and historically such
factors probably caused most of the height differences between
the poorer and richer strata of the population. The increasing
wealth in many societies has led to dramatic reduction in
starvation and infectious disease.5 Still the accumulated results
of social and material disadvantage during foetal life and
658
STRONG POSITIVE ASSOCIATION BETWEEN HEIGHT AND EDUCATIONAL ACHIEVEMENT
childhood may be responsible for a substantial part of the height
differences between various groups in society.6
Both family7 and twin-studies show that height is a highly
genetic trait in modern Western societies, with heritability
(proportion of variance attributable to additive genetic effects)
close to 0.90 in males and 0.75 in females.8 However, it does not
follow from this that height differences between social groups
are determined by genetic factors. It is somewhat puzzling that
socioeconomic disparities in height seem to be persisting in
Western societies in spite of greatly improved nutrition and
lower occurrence of severe infectious diseases.9 It is of note that
the literature is not unanimous and some studies have reported
decreasing social disparities in height.10
Previous research on associations between height and
socioeconomic position has generally focused on the influence
of social and environmental factors on growth and adult
height. However, in the light of the very high heritability of
height in modern societies, we argue that it is relevant to
investigate how height may influence future social outcomes.
One of the most important indicators of social position is
educational level. We have been able to study how height in
young adulthood predicts attainment of high (university level)
education in later life in a very large cohort of Swedish men
born 1950–75. In our analyses we have been able to adjust for
parental socioeconomic position, shared family environmental
factors, and logical cognitive ability of cohort members.
Methods
Information on this study sample was obtained by linkages of
the following Swedish national registers: the Multi-Generation
Register (MGR), the Military Service Conscription Register
(MSCR), and the Population and Housing Censuses (PHC) of
1970–2000. From the MGR all non-adopted males born in
Sweden between 1950 and 1975 with information on their
parents (n 5 1 373 122) were identified. Of these men, 1 189 190
(86.6%) had a record in the MSCR. After removal of outliers
(inclusion criteria weight 40–250 kg, height 130–225 cm) and
individuals with missing conscription data (height, logical
cognitive test score, date of conscription, or conscription centre),
the number of men included were 1 080 189. The Swedish
military service conscription examination is required by law and
performed at age 18. Foreign citizenship, or severe chronic
medical condition, or a handicap documented in a medical
certificate, are the only reasons accepted for non-participation.
The logical cognitive test has been described elsewhere.11
Information on the educational achievement up to the year
2000 was available for 1 044 462 of the included conscripts
surviving and remaining in the country to that year. Maternal
and paternal education, and occupation were used as indicators
of socioeconomic position of the conscripts. Lack of information
on socioeconomic position reduced the set of individuals
with complete information to 951 219, constituting the material
on which the analyses are performed. Association between
height at conscription and probability of reaching at least 1 year
of university level education (called higher education) by year
2000 was investigated by stratified analyses of higher education
by birth-year and height in 5 cm intervals. Estimation of effect
sizes and adjustments for possible confounding were done by
logistic regression (LOGISTIC procedure in SAS version 8.2).
659
Possible confounding from year of birth, conscription test centre,
logical cognitive test score, and parental social position was
investigated. Two measures of parental social position were used
(i) the highest socioeconomic index (SEI) of either parent
by the time of the conscription (eight categories: unskilled
workers, skilled workers, farmers and self employed, lower level
civil servant, middle level civil servant, higher civil servant,
leading or free academic position, and other); and (ii) duration
of maternal and paternal education (six categories: ,9 years
of primary school, 9 years of primary school, ,3 years
of secondary school, 3 years of secondary school, ,3 years of
higher education, and 3 or more years in higher education).
The highest recorded level from PHC 1970–2000 was used for
each parent. Within brother-pair analyses were performed by
conditional logistic regression using the PHREG procedure in
SAS version 8.2. Among all first-born full brothers, pairs
discordant for higher education at year 2000 (n 5 46 199 pairs)
were selected for analysis. The association between height and
being the higher educated brother within each pair was then
estimated.
Results
The mean height of eligible individuals (n 5 951 219) at
conscription was 179.2 cm (standard deviation 5 6.4 cm). A total
of 306 424 conscripts (32%) had obtained at least 1 year of
higher education by the year of 2000.
The probability of achieving higher education later in life
increases linearly with height. This can be clearly seen by
plotting the fraction of men with higher education against
height at conscription (in 5 cm categories) and birth-year (in
5 year birth-cohorts) (Figure 1). Strong relations between height
and higher education are found in all birth-strata. For example,
among men born 1950–55 the fraction with higher education
by year 2000 is 15% for men shorter than 165 cm as compared
with 45% for men taller than194 cm. Inverse relations of
similar strength was observed when the fraction of men having
only primary schooling at year 2000 was analysed against
height at conscription in 5 cm categories (data not shown).
Confounding from secular trends, geographic variation,
parental education and SEI, and logical cognitive performance
of index subjects was investigated using logistic regression
(Table 1). In the unadjusted model (A), the OR for higher
education is 3.5 between the tallest and the shortest category.
The trend is linear with an increase in OR of 21% for each 5 cm a
conscript is taller. Adjustment for birth-year and conscription
test centre had practically no effect on the association (Model B),
ruling out confounding due to secular or geographic variation.
Parental socioeconomic confounding was studied by
including into the model the educational level and SEI of
parents at the time of conscription (Model C). This resulted in a
slight attenuation of the association between height and higher
education, with the OR (95% CI) per 5 cm increase in height
going from 1.21 (1.20–1.21) to 1.16 (1.15–1.16). Thus, a minor
part of the height association can be explained by disparities in
family socioeconomic background in this cohort.
To assess whether intelligence mediates the association
between height and education, we adjusted for logical
cognitive performance, which is a measure of IQ obtained at
conscription examination (Model D). This attenuated the
660
INTERNATIONAL JOURNAL OF EPIDEMIOLOGY
Year of
1971-75
1966-70
1961-65
1956-60
birth
1950-55
50
45
40
35
30
25 %
20
15
10
5
0
>194
185- 190175- 180194 cm
170189
< 165 165- 174 179 184
cm cm
cm 169 cm cm cm
Height
cm
Figure 1 Proportion of men with higher education in year 2000, by year of birth and height at age 18 years
Table 1 Associations (OR, 95% CI) of height with higher education
n (%)
Model A
unadjusted
Model B
(adjusted for
year of birth,
conscription test
centre)
Model C
(model B plus
parental education
and SEI)
Model D
(model C plus
logical cognitive
performance)
Height (cm)
,165
10 176 (1.1)
1 (REF)
1 (REF)
1 (REF)
1 (REF)
165–169
49 734 (5.2)
1.29 (1.22–1.36)
1.29 (1.22–1.36)
1.21 (1.14–1.28)
1.06 (0.99–1.13)
170–174
161 340 (17.0)
1.65 (1.56–1.74)
1.65 (1.56–1.73)
1.48 (1.41–1.57)
1.20 (1.13–1.27)
175–179
273 846 (28.8)
2.01 (1.91–2.12)
2.00 (1.90–2.11)
1.74 (1.64–1.83)
1.32 (1.24–1.40)
180–184
260 394 (27.4)
2.42 (2.30–2.55)
2.40 (2.28–2.53)
2.00 (1.89–2.11)
1.44 (1.35–1.52)
185–189
140 700 (14.8)
2.87 (2.72–3.02)
2.84 (2.70–3.00)
2.27 (2.15–2.40)
1.57 (1.48–1.66)
190–194
44 961 (4.7)
3.28 (3.10.3.46)
3.24 (3.06–3.41)
2.50 (2.36–2.65)
1.68 (1.58–1.79)
.194
10 068 (1.1)
3.50 (3.28–3.73)
3.44 (3.22–3.66)
2.54 (2.38–2.72)
1.65 (1.53–1.78)
1950–55
177 591 (18.7)
1.25 (1.24–1.26)
1.25 (1.24–1.26)
1.20 (1.19–1.21)
1.12 (1.11–1.13)
1956–60
169 768 (17.9)
1.24 (1.23–1.25)
1.24 (1.23–1.25)
1.18 (1.17–1.19)
1.11 (1.10–1.12)
1961–65
216 755 (22.8)
1.21 (1.20–1.22)
1.21 (1.20–1.22)
1.16 (1.15–1.17)
1.10 (1.09–1.11)
1966–70
165 004 (17.4)
1.18 (1.17–1.19)
1.18 (1.17–1.19)
1.14 (1.13–1.15)
1.09 (1.08–1.10)
1971–75
222 101 (23.4)
1.17 (1.16–1.18)
1.17 (1.16–1.18)
1.12 (1.11–1.13)
1.06 (1.06–1.07)
951 219 (100)
1.21 (1.20–1.21)
1.21 (1.20–1.21)
1.16 (1.15–1.16)
1.10 (1.09–1.10)
NA
0.0001
0.0001
0.0001
Linear effect of 5 cm height increment
Birth cohort
All men
Interaction height X year of birth, P ,
association further, with a decrease in OR per 5 cm increase in
height from 1.16 to 1.10 (1.09–1.10). This reduction in OR is of
similar size as that observed after adjustment for parental
socioeconomic position. Thus, the relation between logical
cognitive performance and height does to a significant degree
contribute to the height—higher education association.
The important question of whether the association between
height and education has diminished over time was tested by
performing separate analyses for each 5-year birth-strata. The
association is less pronounced in later birth-years (Table 1),
and the interaction term between height and year of birth is
significant in all adjusted models.
We then tested if inter-generational transmission of height
effects on education is evident by estimating the probability of
higher education as a function of height among biological
fathers. Our dataset contains information on height at conscription for men born between 1950 and 1975. For a subset of
conscripts born during the later years information was available
on their fathers height (n 5 14 321). The association of height
in these fathers and higher education by year 2000 among
their sons was examined. Sons of tall fathers had increased
chances of reaching higher education (Table 2). For each 5 cm
increase in height in the fathers, the OR increases with 15%;
birth year and conscript centre adjusted OR 5 1.15 (1.11–1.19).
STRONG POSITIVE ASSOCIATION BETWEEN HEIGHT AND EDUCATIONAL ACHIEVEMENT
Table 2 Association between height in father and higher education
in son
661
Table 3 Association between height and higher education within full
biological brother-pairs discordant for higher education
OR (95% CI) of
being the higher
educated brother
per 5 cm
Adjustment variables
OR (95% CI) of
higher education
in son per 5 cm
in father
Year of birth, test-centre
1.15 (1.11–1.19)
Unadjusted
1.14 (1.12–1.16)
Year of birth, test-centre,
parental education and SEI
1.07 (1.03–1.10)
Year of birth, test-centre
1.14 (1.13–1.16)
Year of birth, test-centre,
logical cognitive performance
1.08 (1.07–1.10)
Year of birth, test-centre,
parental education, SEI and
logical cognitive performance
1.03 (0.99–1.0)
After adjustment for parental education and SEI the effect
of father’s height was reduced by approximately one-half
[OR per 5 cm increase in height being 1.07 (1.03–1.10). Further
attenuation was evident when logical cognitive performance
of the son was included in the model (OR 5 1.03 (0.99–1.08)].
A powerful test to analyse if the association between height
and higher education solely relies on familial factors is to
examine if the association holds also within brother-pairs. All
available pairs of first-born and second-born non-twin biological
sons of each mother—father combination, in total n 5 168 701
pairs, were identified. Pairs in which the brothers were discordant for higher education were then selected (n 5 46 199
pairs) for analysis. The OR of being the higher educated brother
was 1.14 (1.12–1.16) per 5 cm difference in height in both
the unadjusted model and in the model adjusting for year
of birth and test centre (Table 3). The OR was attenuated to
1.08 (1.07–1.10) upon further adjustment for logical cognitive
performance.
Discussion
Although relationships between body size and social variables
have been well documented previously we believe the results
of the present investigation provide new insights in a number
of ways. The strength of the association is remarkable, with
a 2- to 3-fold difference in the probability of achieving
higher education among tall (.194 cm), compared with short
(,165 cm) men. A previous study on height stereotypes has
suggested that being short would be more of a liability to less
favourable social position than being tall would be an asset.12
The present results do not support this finding for educational
achievement in the examined population of Swedish men.
Instead a marked linearity of the effect is evident, with a
steady increase in higher education with increasing height at
age 18 years.
A number of possible explanations to the observed association
between height and higher education could be assessed by
inclusion of covariates into the analysis. Both height and
education increases somewhat with year of birth. Because
educational achievement is assessed at the same year (2000) for
all cohort members, year of birth is by design strongly related
to the number of years each individual has been monitored for
the attainment of higher education. Geographic differences in
height are small, but in education somewhat larger. Inclusion
of birth-year and geographic information into the model
left the estimates materially unchanged, showing that secular
trends or geographic variation are unlikely causes of the
Adjustment variables
association. Height is related to other measures of body size,
which in turn are likely to be related to social position and
education (but not the focus of this study). We tested the effects
of including body weight into the model. A marked augmentation of the association was observed (data not shown),
indicating that height is likely to be the prime dimension of body
size responsible for the positive relation between size and
education.
Socioeconomic factors of raising environment, as reflected
by the socioeconomic position of parents during childhood, are
well known to be related to both growth and educational
achievement.1,13 Detailed adjustments for the parental social
position are, therefore, important. By including the highest
reported occupational level of either mother or father together
with the educational level of both the mother and the father
into the model the possible confounding from these socioeconomic aspects of the upbringing were investigated. When
socioeconomic level during childhood were controlled the
association became somewhat weakened with a drop in OR
per 5 cm from 1.21 to 1.16. We conclude that a minor fraction
of the association between height and education can be
explained by differences in parental socioeconomic position.
Graduation marks from secondary school has during the
covered study time been an important criteria for entering a
higher education in Sweden. Cognitive abilities influence
school results, which in turn influence graduation marks from
primary and secondary schools. Height is related to measures
of intelligence.14–16 Since head and brain size are positively
correlated to intelligence17–19 and height in turn is correlated
to head size,20 it might be speculated that height is related
to likelihood of higher education, through some biological
pathway acting via brain size and intelligence. To test whether
intelligence contributes to the association between height and
higher education, logical cognitive ability by the time of
conscription was entered into the model. After this adjustment
the association was reduced, indicating that a minor part of the
positive effect of height for the chances to achieve higher
educational later in life can be explained by increased
cognitive ability among taller men by the age of 18. Since
cognitive ability is the product of both the genetic potential of
an individual as well as training by schooling, variation in
schooling up to the age of 18 in itself clearly must affect
cognitive ability testing results. One twin study has previously
suggested that the correlation between height and education is
not due to overlapping genes behind both traits.4 A recent
study on Norwegian male twins found on the other hand a
significant proportion (0.35) of the correlation between height
662
INTERNATIONAL JOURNAL OF EPIDEMIOLOGY
and intelligence to be due to overlapping genetic factors.21 The
mechanisms underlying the influence of cognitive ability on
the association between height and education remain to be
clarified.
The association between height and higher education
diminishes somewhat with year of birth. This is in agreement
with a diminishing role over time of influences of poverty and
social disadvantage on foetal and childhood growth such as
under-nutrition and infectious disease. Still, strong associations
remain also for men born in the 1970s.
Since height has a clear genetic basis in modern society, tall
individuals generally have tall parents. The probability of
higher education among men coming from tall as apposed to
short families should, therefore, be increased. This was
investigated by using height of biological father as an indicator
of ‘familial height’. Strong associations between height of the
father and own achievement of higher education were
evident. After adjustment for parental education and SEI,
the strength of the association was reduced by one half,
showing that most of the transmission of effects of height on
education is abolished when socioeconomic factors were taken
into account. When cognitive performance of the son was also
included into the model the effect of paternal height was no
longer significant. The bulk of the effect of having a tall father
can thus be explained by socioeconomic and cognitive factors.
There is little reason to believe that starvation or disease
constitutes the mechanism by which socioeconomic background influences the relation between height and education
in the investigated population. A general view is instead that
such influence comes from accumulated results of social and
material conditions during foetal life and childhood.6 It should
be mentioned that even if we have used the most detailed
information on socioeconomic position available, there might
still be residual confounding from socioeconomic variation
between families not captured by the variables included in the
ordinary logistic regression models. Conditional logistic
regression was, therefore, used to test the association within
biological full-brother-pairs discordant for higher education.
The results show that the taller of the two brothers also tended
to be the one with the higher education. This still holds true
after adjustment for birth-order (birth year) and logical
cognitive performance. We interpret this result as evidence
for non-familial mechanisms contributing to the association
between height and education.
An alternative pathway through which socioeconomic
background influences the relation between height and
education may be culturally founded co-variation of height
and socioeconomic position over generations. Tallness is clearly
of social advantage for males in most populations.12,13 Tall men
are, for example, preferred as dates22 and employees.12 Of
special interest here are findings showing that prejudices about
competence among children are influenced by height. Taller
boys are perceived as more competent than shorter boys of the
same age in school environments from preschool onwards.12
Even after secular, geographic, socioeconomic, cognitive, and
general familial factors have been accounted for, height
remained positively associated with higher education. Various
types of inequalities exist in society. Discrimination owing to
sex, ethnic origin, weight (obesity), and age are well-known
examples. This study suggests that height may be an additional
member on this list although residual confounding cannot be
ruled out.
KEY MESSAGES
In spite of greatly improved nutrition and lower occurrence of infectious diseases, socioeconomic disparities in
height seem to be persisting in Western societies.
Parental socioeconomic position and intelligence are confounding the association between height and education to
a similar extent but a significant association remains also after these covariates are taken into account.
The relationship between height and attainment of higher education in later life diminishes somewhat with
birth-year.
Evidence for non-familial mechanisms contributing to the relation between height and education comes from
persisting associations also within brother-pairs.
References
1
2
3
4
5
Meyer HE, Selmer R. Income, educational level and body height.
Ann Hum Biol 1999;26:219–27.
6
Walker M, Shaper AG, Wannamethee G. Height and social class
in middle-aged British men. J Epidemiol Community Health 1988;
42:299–303.
7
Judge TA, Cable DM. The effect of physical height on workplace
success and income: preliminary test of a theoretical model. J Appl
Psychol 2004;89:428–41.
Silventoinen K, Kaprio J, Lahelma E. Genetic and environmental
contributions to the association between body height and educational
attainment: a study of adult Finnish twins. Behav Genet 2000;30:
477–85.
8
9
Padez C. Stature and stature distribution in Portuguese male adults
1904–1998: the role of environmental factors. Am J Human Biol
2002;14:39–49.
Kuh D, Wadsworth M. Parental height: childhood environment
and subsequent adult height in a national birth cohort. Int J Epidemiol
1989;18:663–68.
Brown WM, Beck SR, Lange EM, Davis CC, Kay CM, Langefeld
CD et al. Age-stratified heritability estimation in the Framingham
Heart Study families. BMC Genet 2003;4 (Suppl 1):S32.
Silventoinen K, Sammalisto S, Perola M, Boomsma DI, Cornes BK,
Davis C et al. Heritability of adult body height: a comparative study of
twin cohorts in eight countries. Twin Res 2003;6:399–408.
Cavelaars AE, Kunst AE, Geurts JJ, Crialesi R, Grotvedt L, Helmert U
et al. Persistent variations in average height between countries
STRONG POSITIVE ASSOCIATION BETWEEN HEIGHT AND EDUCATIONAL ACHIEVEMENT
and between socio-economic groups: an overview of 10 European
countries. Ann Hum Biol 2000;27:407–21.
10
11
12
13
14
15
Peck AM, Vagero DH. Adult body height and childhood socioeconomic
group in the Swedish population. J Epidemiol Community Health
1987;41:333–37.
Gunnell D, Harrison G, Rasmussen F, Fouskakis D, Tynelius P.
Associations between premorbid intellectual performance, early-life
exposures and early-onset schizophrenia. Cohort study. Br J Psychiatry
2002;181:298–305.
Jackson LA, Ervin KS. Height stereotypes of women and men:
the liabilities of shortness for both sexes. J Soc Psychol 2001;
132:433–45.
16
17
18
19
Silventoinen K. Determinants of variation in adult body height.
J Biosoc Sci 2003;35:263–85.
20
Humphreys LG, Davey TC, Park RK. Longitudinal correlation analysis
of standing height and intelligence. Child Dev 1985;56:1465–78.
21
Abbott RD, White LR, Ross GW, Petrovitch H, Masaki KH,
Snowdon DA et al. Height as a marker of childhood development
and late-life cognitive function: the Honolulu-Asia Aging Study.
Pediatrics 1998;102:602–09.
22
663
Teasdale TW, Owen DR, Sorensen TI. Intelligence and educational
level in adult males at the extremes of stature. Hum Biol 1991;
63:19–30.
Andreasen NC, Flaum M, Swayze V 2nd, O’Leary DS, Alliger R, Cohen
G et al. Intelligence and brain structure in normal individuals.
Am J Psychiatry 1993;150:130–34.
Paradiso S, Andreasen NC, O’Leary DS, Arndt S, Robinson RG.
Cerebellar size and cognition: correlations with IQ, verbal memory
and motor dexterity. Neuropsychiatry Neuropsychol Behav Neurol
1997;10:1–8.
Tisserand DJ, Bosma H, Van Boxtel MP, Jolles J. Head size and
cognitive ability in nondemented older adults are related. Neurology
2001;56:969–71.
Bushby KM, Cole T, Matthews JN, Goodship JA. Centiles for adult
head circumference. Arch Dis Child 1992;67:1286–87.
Sundet JM, Tambs K, Harris JR, Magnus P, Torjussen TM. Resolving
the genetic and environmental sources of the correlation between
height and intelligence: a study of nearly 2600 Norwegian male twin
pairs. Twin Res Hum Genet 2005;8:307–11.
Hensley WE. Height as a basis for interpersonal attraction. Adolescence
1994;29:469–74.
Published by Oxford University Press on behalf of the International Epidemiological Association
Ó The Author 2006; all rights reserved. Advance Access publication 11 May 2006
International Journal of Epidemiology 2006;35:663–664
doi:10.1093/ije/dyl087
Commentary: The associations between
height, cognition, and education and their
relevance for health studies
Denny Vågerö* and Bitte Modin
The study by Magnusson et al.1 very convincingly demonstrates a
close association between height at 18 and achieved education
among Swedish men. The taller a man is the more likely he is to
go to university. The authors suggest that short people may be
discriminated against in the school system. However, they have
no empirical data concerning ‘discrimination’, consequently this
conclusion is left hanging in the air.
Two questions emerge from this well-written paper:
(i) Why are achieved education and height linked to each
other?
Is it due to characteristics of the school system or peer
relations that discriminate against short individuals? Other
research has suggested that this is a possibility, for instance West2
or Nyström Peck.3
Or does this link arise from common social, psychological, or
biological factors, which influence both height and educational
achievement? Magnusson et al. control for many such factors,
for instance parents’ education and family background, but
they also conclude that this possibility cannot yet be ruled out.
CHESS, Centre for Health Equity Studies, Stockholm, Sweden.
* Corresponding author. E-mail: [email protected]
(ii)
What is the implication for health of the association
between height and education?
With regard to the first question there is an analogy with
sociological studies of how social class determines educational
achievement. Two separate effects have been established here:
first, a working-class child tends to have poorer school marks
than a middle-class child—this is referred to as the primary effect
of social class. Second, if one compares individuals with the same
school marks, a working-class child is less likely than a
middle-class child to continue to higher education—this is
referred to as the secondary effect of social class.4 To draw an
analogy with studies of social class, we could in the present case
perhaps talk about a primary effect of height on cognition and a
secondary effect of height on educational achievement when we
compare individuals on the same cognitive level. We assume
that discrimination against short individuals would play a greater
role in the second case. A primary effect of height on cognition
may, instead, suggest that there are common underlying social–
psychological–biological factors.
We replicated the study by Magnusson et al. by using the
Stockholm Birth Cohort Study.5 Thus we studied 5983 men born
in 1953 living in Stockholm in 1963, for whom we have data on