Σάββας Τοκµακίδης, Καθηγητής
Τµήµα Επιστήµης Φυσικής Αγωγής και Αθλητισµού
∆ηµοκρίτειο Πανεπιστήµιο Θράκης
Validity of Self-Reported Anthropometric Values Used to Assess Body
Mass Index and Estimate Obesity in Greek School Children
Savvas P. Tokmakidis, Ph.D.*, Antonios D. Christodoulos, M.Sc., and Nikolaos I.
Department of Physical Education and Sport Science, Democritus University of Thrace, Komotini, Greece
Το άρθρο δηµοσιεύτηκε στο Journal of Adolescent Health 40 (2007) 305–310
Αξιοπιστία των αυτο-αναφερόµενων ανθρωποµετρικών τιµών που
χρησιµοποιούνται για την αξιολόγηση του δείκτη σωµατικής µάζας και
τον προσδιορισµό της παχυσαρκίας σε Έλληνες µαθητές
Σκοπός: Να εξετασθεί η αξιοπιστία των αυτο-αναφερόµενων τιµών σωµατικού ύψους και
βάρους που χρησιµοποιούνται για τον προσδιορισµό του δείκτη σωµατικής µάζας (BMI), ως
διαγνωστική µέθοδος για την εκτίµηση των υπέρβαρων και παχύσαρκων Ελλήνων µαθητών.
Μέθοδος: Το αυτο-αναφερόµενο ύψος και βάρος καταγράφηκε και κατόπιν µετρήθηκε σε 378
παιδιά δηµοτικού (µέση ηλικία 11.4 ± .4 έτη) και 298 γυµνασίου (µέση ηλικία 12.5 ± .3 έτη).
Για την σύγκριση µεταξύ των τιµών που προκύπτουν στον προσδιορισµό των υπέρβαρων και
παχύσαρκων παιδιών από τις αυτο-αναφερόµενες και τις πραγµατικές (µετρηµένες) τιµές
χρησιµοποιήθηκαν οι δείκτες BMI που έχουν υιοθετηθεί από το International Obesity Task
Αποτελέσµατα: Βρέθηκαν σηµαντικές διαφορές ανάµεσα στους αυτό-αναφερόµενους και τους
πραγµατικά µετρηµένους δείκτες σε όλες τις υπο-οµάδες µε εξαίρεση το ύψος στα κορίτσια του
δηµοτικού. Ο βαθµός του αυτό-αναφερόµενου σφάλµατος δεν διέφερε µεταξύ των φύλων.
Παρόλα αυτά όµως ήταν υψηλότερο στους µαθητές του γυµνασίου και στα πιο βαριά παιδιά σε
σχέση µε τα παιδιά του δηµοτικού και τα ελαφρύτερα παιδιά αντιστοίχως. Με βάση τις αυτό-
αναφερόµενες καταγραφές οι εκτιµώµενες τιµές ήταν 23.1% για τα υπέρβαρα και 4.3% για
παχύσαρκα, αλλά σύµφωνα µε τις µετρήσεις οι αντίστοιχες τιµές ήταν 28.8% και 9.5%
Συµπεράσµατα: Τα ευρήµατα υποδηλώνουν ότι η παρατηρούµενη ασυµφωνία µεταξύ των
αυτο-αναφερόµενων και των πραγµατικά µετρηµένων τιµών στους Έλληνες εφήβους και παιδιά
µπορεί να οδηγήσει σε λανθασµένη εκτίµηση του υπερβολικού βάρους και της παχυσαρκίας.
Παρότι τα δεδοµένα µέσω του αυτο-προσδιορισµού είναι εύκολα στην συλλογή τους, οι ιατρικές
έρευνες που αφορούν το υπερβολικό βάρος και την παχυσαρκία στους νέους χρειάζονται πιο
ακριβείς και αξιόπιστες µεθόδους.
Obesity has become a worldwide epidemic in all segments of the population in recent years
[1,2]. The prevalence and severity of overweight and obesity is also increasing in children and
adolescents . Obesity in early life is of particular importance due to its short- and long-term
association with morbid outcomes and its influence on young people’s psychosocial
development [4,5]. In most cases, childhood overweight and obesity track into adult life ,
implying a substantial increase in life style diseases such as type II diabetes, hypertension,
and cardiovascular disease [7,8]. Therefore, the identification and monitoring of overweight or
obese children and adolescents are major concerns in public health.
The most commonly used measurement of body composition is the body mass index (BMI),
defined as body weight divided by height squared (kg.m-2). Given its strong association (r =
.83 – .98) with adiposity measurements derived from dual energy x-ray absorptiometry in
children , BMI appears to be an appropriate measurement for the indirect assessment of
adiposity in childhood and adolescence [10,11].
Alternatively to actual anthropometric measures, large scale studies like the Health Behaviour
in School-Aged Children [12,13], frequently use self-reported height and weight for practical
and financial reasons. The BMI derived from these reports is subsequently used to screen
weight problems. However, most of the studies that have examined the accuracy of self-
reported height and weight have shown inconsistent outcomes. Some studies suggest that
adolescent self-reports of height and weight, are valid , while others have raised concern
about the accuracy of self-reported anthropometric values in adolescence [15–18].
Furthermore, the validity of self-reported height and weight has not been adequately
evaluated in diverse samples of youth, especially in different cultural contexts. Because BMI
values may vary among different ethnic groups , these differences might result in greater
inaccuracy for ethnic populations with higher BMI values [20 –22].
Evidence of existing research using actual anthropometric measures indicates that childhood
obesity has increased alarmingly throughout Greece in the last decades, and the current
prevalence of overweight and obesity among Greek children and adolescents is one of the
highest in Europe [23–26]. Contrary to these reports, and based on self-reported data
obtained from a nationwide sample of Greek school-aged children, Karayiannis et al 
concluded that the prevalence of childhood obesity is lower in Greece, compared to most other
western countries. It is worth mentioning that only one study has investigated the accuracy of
self-reported height and weight in Greek adolescents , while no validity study exists for
primary school children. Thus, the patterns of height and weight validity of Greek children and
adolescents have yet to be further evaluated. The purpose of the present study was to
examine the validity of self-reported body measures as a diagnostic method for the evaluation
of overweight and obesity in Greek children and adolescents.
Three secondary schools located in the metropolitan area of Athens and 15 elementary
schools in the province of North Attica, Greece, were randomly selected. Prior to the
commencement of the study, permission from the school principal was obtained and parental
consent was secured. All students of the above schools were asked to participate into the
study. A total number of 378 healthy elementary school pupils (197 girls, 181 boys, mean age
11.4 ± .4 years, participation rate 96.2%) and 298 high school students (152 girls, 146 boys,
mean age 12.5 ± .3 years, participation rate 97.3%) obtained written parental consent, after
full explanation of the testing procedures. The research ethics committee of Democritus
University of Thrace approved the investigation. All measurements were conducted during
morning school visits by experienced investigators using identical protocols. The demographic
data of the study populations are shown in Table 1. The participants represented ethnic
groups as they occur in the Greek population (92.3% Greek origins vs. 7.7% non-Greek
origins), whereby most of the foreign students come from immigrant families, primarily from
Albania and East Europe .
Assessments took place on two different days in classroom settings. During the first session,
students were asked to report their demographic information (date of birth, ethnicity, parental
education, height, and weight). Participants were not told that their actual height and weight
values would be subsequently verified. Age was derived from the date of interview minus the
date of birth. On the second session, trained staff measured all students who attended the
school classes according to the measurement protocol. Students were weighed on an
electronic scale to the nearest .5 kg, lightly dressed and barefooted. Standing height was
measured to the nearest .5 cm with shoes off, feet together, and head in the Frankfort
horizontal plane. BMI was calculated on both self-reported and measured height and weight.
Overweight and obesity were identified using age- and gender-specific international cut-off
points , based on average centiles estimated to pass through BMI values of 25 and 30
kg.m_2 respectively, at the age of 18. These cut-off points have been widely used in studies
with children and adolescents .
SPSS version 11.0 for Windows (Chicago, IL) was used for data management and statistical
calculations. Descriptive means and frequencies were generated. Pearson correlation
coefficients analyses were performed, while the student paired t-tests were used to determine
group differences for continuous variables (differences in self-reported vs. measured height,
weight, and BMI). Comparisons between continuous and categorical variables were performed
by unpaired t-tests and analysis of variance (ANOVA), to examine if the assessed differences
were influenced by gender, age, or BMI status. χ2 tests were used to determine significant
differences in the estimating rates of overweight and obesity determined by self-reported
versus measured BMI. All reported p-values were compared to a significance level of 5%.
Comparisons between self-reported height and weight measured and used to assess BMI
adjusted by gender and age group
Note: Values significantly different compared to self-reported data at † p < .005 and ‡ p <
.001. Differences between subgroups within the same gender significant at * p < .05, § p <
.005 and # p < .001. No differences were detected between genders within the same age
group (p > .05).
High correlations were found between self-reported and measured anthropometric indices: r =
.91 (height), r = .96 (weight), and r = .90 (BMI), p < .001. However, paired t-test analysis
revealed significant differences between the self-reported and actual measurements in all
subgroups, except for height in elementary school girls (Table 2). Independent t-test analysis
revealed that the degree of self-report bias did not differ between boys and girls for height
(t(644) = -.26, p < .797), weight (t(652) = -.69, p < .488) or BMI (t(638) = -.43, p < .665).
Significant differences were found between age groups. High school students tended to
overestimate their height and under-report their weight to a greater degree than elementary
school pupils. As a result, the understating of BMI was greater for high school students
compared to elementary school pupils (mean difference in measured vs. reported BMI = 1.61
± 1.4 kg.m_2 versus .79 ± 1.8 kg.m_2; p < .001).
As shown in Figure 1, the ANOVA results revealed a significant effect of BMI status in the
accuracy of self-reported parameters, with a higher BMI resulting in trivial discrepancies of
height (F(2, 644) = 5.39, p < .005), and in considerable biases of weight (F(2, 644) = 71.10,
p < .001) and BMI (F(2, 644) = 74.91, p < .001). The same pattern was observed when
differences were computed for elementary pupils and high school students separately (Figure
Figure 1. Differences between self-reported and measured values of height, weight, and BMI
across BMI categories. Values significantly different: † vs. overweight (p-values between .004
and .001); ‡ vs. obese (p-values between .02 and .001).
Figure 2. Estimating rates of overweight and obesity by age group, according to self-reported
and actual anthropometric data.
Based on self-reports, prevalence estimates were 23.1% for overweight and 4.3% for obesity,
but according to measured data, the corresponding rates were 28.8% and 9.5%, respectively
(χ2 = 541.49, p = .001). Self-reports led to the underestimation of overweight by 5.7% and
obesity by 5.2%, whereby the magnitude of the underestimation varied between elementary
pupils and high school students (Figure 2).
In health surveys, actual measurements are frequently replaced by self-reported height and
weight, which are subsequently used to provide a categorical measure of overweight and
obesity by applying cut-off points in BMI. The present study was undertaken to evaluate the
validity of these data as an indicator of overweight and obesity in Greek children.
Our results revealed significant differences between self-reported and actual measures in both
genders and age groups. Discrepancies in self-reported height by students in Greece were
either trivial (-.6 cm for primary school) or significant (-.3 cm for high school). On the other
hand, biases in weight were significant and of considerable size for the total sample (Table 2).
These findings are in accordance with previous studies reporting that children and adolescents
tend to overestimate their height and underestimate their weight [21, 28, 32]. The overall
mean difference of weight (2.0 kg) in the present study is lower than that reported for
American adolescents , higher compared to Welsh adolescents , and similar to that
observed by other studies among Australian , Italian , and Greek teenagers .
In line with previous reports [16, 17, 33], we found that the patterns of accuracy in self-
reported anthropometric measures are not influenced by gender, although not all surveys
have agreed with these findings . On the contrary, our data indicate that the accuracy of
self-reports varied significantly by age, whereby high school students over-reported their
height and understated their weight more than their younger counterparts. We further found
that the magnitude of the discrepancy between self-reported and actual anthropometric
measures was affected by the actual body size, with heavier students understating their
weight more than thinner students. The latter is a notable consistent finding in the literature
[16, 28, 33, 36, 37]. Although it is clearly an objective, measurable phenomenon (i.e., BMI),
obesity is also a subjective, emotional experience of one’s body and body image, and has
been significantly associated with internal states, such as low self esteem [38, 39]. Because a
lower self esteem is associated with greater bias in self-reported weight , discrepancies in
self-reports of weight problems at pre-pubescent and first puberty phase possibly reflect
discrepant perceptions of body image among individuals, implying one’s unwillingness or
inability to acknowledge his/her obesity because of denial and/or social stigma .
Regardless of significant or non-significant differences, self-reports and actual measures were
highly correlated, implying that the correlation coefficient does not secure validity. Thus,
making inferences about the validity of self-reported data by relying solely on the correlation
coefficient might be misleading . Although this coefficient does not seem to provide
valuable information about the discrepancy between self-reported and actual measures, some
studies based only on high correlation coefficients suggest that self-reported height and
weight are valid proxy measures for actual measures, especially in analyses that use these
values as continuous variables [14, 21].
However, when BMI values are used for classification into BMI categories (normal weight,
overweight, and obese), basing BMI on self-reports clearly leads to underestimates of the
prevalence of weight problems. For example, in the study of Brener et al , the self-report
screen for obesity showed just 54.9% sensitivity, failing to detect a substantial proportion of
morbid cases. In our study, the self-report screen missed 41.5% of overweight and 57.8% of
obesity cases, leading to an underestimation of overweight and obesity by 3.7% and 5.8%,
respectively, for elementary school, and 8.4% and 4.4%, respectively, for high school
students. The magnitude of underestimation for the total sample is compared with that
reported for overweight (4.8%) and higher than that reported for obesity (1.6%) in Welsh
adolescents . These differences imply that self-reported data derived from children and
adolescents might not be as valid as the data obtained from actual measurements, calling into
question the use of self-reports in these age groups as a screen for overweight and obesity.
For instance, using self-reported data derived from a nationwide sample of Greek school-aged
children , the estimating rates for adiposity problems were 15.3% for overweight and
1.8% for obesity, contradicting the corresponding prevalence estimates for overweight (21.6–
30.3%) and obesity (5.6–9.5%) reported by previous studies based on actual measures from
children and adolescents from several Greek regions [23–25] (Figure 3).
Figure 3. Prevalence rates of overweight and obesity in several districts of Greece, according
to published data [23–25,27]. Note: Prevalence rates of nationwide sample (Karayiannis et al.
2003) are based on self-reported anthropometric data.
To overcome this shortcoming, it has been suggested that future large-scale studies should
take measured data from at least a random sub-sample to examine the size and direction of
bias  as well as to identify the sources of this bias. Identified sources of bias can be
entered into adequate models as explanatory variables along with reported values and the
derived function can then be applied to minimize the bias .
Our study has some limitations: a strictly random sampling of all eligible students was
virtually impossible; the study was dependent on the principals’ disposal and the process of
informed consent, which was based on the willingness of individual children and their parents
to participate. The prevalence of overweight and obesity, however, was similar to that
reported for school-aged children from other districts of Greece [23–25]. Furthermore, the
sample size and the age range of our sample, limit the generalization of our findings.
Despite the above limitations, the high prevalence rates of overweight and obesity observed in
our sample offer some support on the growing obesity prevalence in Greek children and
adolescents, underlining the need for continuous and accurate monitoring of excess adiposity
problems in youth. The present findings indicate that there is a considerable discrepancy
between self-reported and measured anthropometric data in Greek children and adolescents,
which might have significant consequences in the accuracy of a self-report screen and could
lead to erroneous estimating rates of overweight and obesity. Identifying sources of bias and
using accuracy checks of self-reported data may improve health surveys of overweight
problems in youth.
Future research should involve a wider age range, a larger sample population, and explore
predictors of inaccuracy, to elucidate trends in biases from self-reported anthropometric
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