The authors have declared that no competing interests exist.
Conceived and designed the experiments: WSL SYH KKM THL. Performed the experiments: WSL SYH KKM. Analyzed the data: WSL. Contributed reagents/materials/analysis tools: SYH THL. Wrote the paper: WSL SYH.
To compare the performance of Stunkard’s current body size (CBS) with self-reported body mass index (BMI), waist circumference (WC) and waist to stature ratio (WSR) in predicting weight status in Chinese adolescents, and to determine the CBS cutoffs for overweight/obesity and underweight.
This cross-sectional study was conducted in a sample of 5,418 secondary school students (45.2% boys; mean age 14.7 years). Height and weight were measured by trained teachers or researchers. Subjects were classified as underweight, normal weight, or overweight/obese according to the International Obesity Task Force cutoffs. Subjects were asked to select the figure that best resembled their CBS on the Stunkard’s figure rating scale. Self-reported height, weight, WC and WSR were also obtained. The performance of CBS, self-reported BMI, WC and WSR as a weight status indicator was analysed by sex-specific receiver operating characteristic curves. The optimal CBS cutoffs for underweight and overweight/obesity were determined based on the Youden Index.
Apart from self-reported BMI, CBS had the greatest area under curve (AUC) for underweight in boys (0.82) and girls (0.81). For overweight/obesity, CBS also had a greater AUC (0.85) than self-reported WC and WSR in boys, and an AUC (0.81) comparable to self-reported WC and WSR in girls. In general, CBS values of 3 and 5 appeared to be the optimal cutoffs for underweight and overweight/obesity, respectively, in different sex-age subgroups.
CBS is a potentially useful indicator to assess weight status of adolescents when measured and self-reported BMI are not available.
Adolescent weight status is commonly defined using body mass index (BMI), which is weight (kg) divided by height squared (m2). When direct measurements of height and weight are infeasible, self-reports are often used. However, over-reporting of height and under-reporting of weight are common
In contrast, figure rating scale is a simple visual tool to assess body image and perceived body size
We have reported that the validity and test-retest reliability of CBS are acceptable in Chinese adolescents
Ethical approval was granted by the Institutional Review Board of the University of Hong Kong/Hospital Authority Hong Kong West Cluster.
The present study is part of a large school-based survey, the Hong Kong Student Obesity Surveillance (HKSOS) project. Details of the sampling method have been reported elsewhere
Among the participating schools, 15 measured anthropometric data of students (n = 6753). After excluding 778 students with incomplete anthropometric data, 309 with extreme self-reported BMI values (<10 kg/m2 or >50 kg/m2)
Height (cm) and weight (kg) were measured barefoot and in light clothing by trained teachers or researchers, following an established protocol
Using the Stunkard’s figure rating scale, the students selected from 9 male or female body figures of increasing size (labelled 1–9) that best resembled their CBS
Based on measured height and weight, weight status was classified as underweight, normal weight, overweight or obese according to the International Obesity Task Force age- and sex-specific BMI cutoffs
Based on measured data, boys were significantly taller (p<0.001), heavier (p<0.001) and had greater BMI (p<0.001) than girls. The overall prevalence of underweight, overweight and obesity in the total sample was 5.7%, 9.9% and 1.2%, respectively (
Boys(n = 2451) | Girls(n = 2967) | ||
Age (years, mean, SD) | 14.7 (1.6) | 14.8 (1.6) | |
Measured data | Height (cm, mean, SD) | 165.0 (9.1) | 157.6 (5.8) |
Weight (kg, mean, SD) | 53.7 (11.3) | 47.7 (7.6) | |
BMI (mean, SD) |
19.6 (3.3) | 19.2 (2.7) | |
Weight status (n, %) |
Underweight | 110 (4.5) | 200 (6.7) |
Normal weight | 1941 (79.2) | 2563 (86.4) | |
Overweight/obesity | 400 (16.3) | 204 (6.9) | |
Overweight | 343 (14.0) | 194 (6.5) | |
Obesity | 57 (2.3) | 10 (0.3) | |
Self-reported data | Height (cm, mean, SD) | 165.4 (9.4) | 157.7 (5.8) |
Weight (kg, mean, SD) | 53.3 (11.2) | 47.0 (7.5) | |
BMI (mean, SD) |
19.4 (3.3) | 18.9 (2.7) | |
WC (cm, mean, SD) |
69.4 (18.0) | 64.6 (17.5) | |
WSR (mean, SD) |
0.42 (0.1) | 0.41 (0.1) | |
CBS (mean, SD) |
4.2 (1.3) | 3.6 (1.0) |
BMI = body mass index.
weight status defined based on IOTF references and measured height and weight.
WC = waist circumference;
WSR = waist to stature ratio;
CBS = current body size.
Apart from BMI (0.89 for boys and 0.88 for girls), CBS had the greatest AUC in both boys (0.82) and girls (0.81) for underweight (
Apart from BMI, CBS had the greatest AUC in both boys and girls. (A) AUC for boys: self-reported BMI (0.89); CBS (0.82); self-reported WC (0.72); self-reported WSR (0.70). (B) AUC for girls: self-reported BMI (0.88); CBS (0.81); self-reported WC (0.77); self-reported WSR (0.76).
Self-reported BMI had the greatest AUC for both sexes. In boys, CBS had a higher AUC than WSR and WC, while in girls the AUCs of CBS, WSR and WC were comparable. (A) AUC for boys: self-reported BMI (0.89); CBS (0.85); self-reported WC (0.80); self-reported WSR (0.78). (B) AUC for girls: self-reported BMI (0.90); CBS (0.81); self-reported WC (0.82); self-reported WSR (0.82).
Based on the Youden index, CBS values of 3 and 5 appeared to be the optimal cutoffs in general for underweight and overweight/obesity, respectively, in different sex-age subgroups (
Age (years) | Underweight | Overweight/obesity | ||||||||||
n (%) | CBS | Sensitivity | Specificity | J | LR+ | CBS | Sensitivity | Specificity | J | LR+ | ||
Boys | All | 2451 | 3 | 0.748 | 0.764 | 0.512 | 3.2 | 5 | 0.870 | 0.690 | 0.560 | 2.8 |
12–<13 | 359 (14.6) | 3 | 0.696 | 0.882 | 0.578 | 5.9 | 5 | 0.788 | 0.734 | 0.522 | 3.0 | |
13–<14 | 522 (21.3) | 3 | 0.697 | 0.792 | 0.488 | 3.3 | 5 | 0.856 | 0.742 | 0.597 | 3.3 | |
14–<15 | 527 (21.5) | 3 | 0.779 | 0.850 | 0.629 | 5.2 | 5 | 0.900 | 0.689 | 0.589 | 2.9 | |
15–<16 | 468 (19.1) | 3 | 0.759 | 0.737 | 0.496 | 2.9 | 6 | 0.762 | 0.889 | 0.651 | 6.9 | |
16–<17 | 338 (13.8) | 3 | 0.811 | 0.500 | 0.311 | 1.6 | 5 | 0.973 | 0.671 | 0.644 | 3.0 | |
17–<18 | 237 (9.7) | 3 | 0.758 | 0.900 | 0.658 | 7.6 | 6 | 0.619 | 0.898 | 0.517 | 6.1 | |
Girls | All | 2967 | 3 | 0.580 | 0.885 | 0.465 | 5.0 | 5 | 0.652 | 0.873 | 0.525 | 5.1 |
12–<13 | 455 (15.3) | 2 | 0.830 | 0.645 | 0.475 | 2.3 | 5 | 0.500 | 0.954 | 0.454 | 11.0 | |
13–<14 | 577 (19.4) | 3 | 0.538 | 0.935 | 0.474 | 8.3 | 5 | 0.672 | 0.894 | 0.566 | 6.3 | |
14–<15 | 581 (19.6) | 3 | 0.901 | 0.611 | 0.512 | 2.3 | 5 | 0.654 | 0.873 | 0.527 | 5.2 | |
15–<16 | 571 (19.2) | 3 | 0.625 | 0.814 | 0.439 | 3.4 | 5 | 0.774 | 0.850 | 0.624 | 5.2 | |
16–<17 | 413 (13.9) | 3 | 0.643 | 0.906 | 0.549 | 6.9 | 5 | 0.650 | 0.842 | 0.492 | 4.1 | |
17–<18 | 370 (12.5) | 3 | 0.658 | 0.889 | 0.547 | 5.9 | 5 | 0.800 | 0.816 | 0.616 | 4.4 |
CBS: current body size; J: Youden index; LR+: positive likelihood ratio.
CBS, self-reported BMI, WC and WSR all predicted weight status reasonably well with AUCs over 0.70. As expected, self-reported BMI had the greatest AUC because a BMI-derived weight status standard was adopted. As such, self-reported BMI was more of a reference for the greatest achievable AUC. Among the other measures, CBS was apparently the best, having the greatest AUC for underweight in boys and girls. It also had a greater AUC than self-reported WC and WSR for overweight/obesity in boys, and an AUC comparable to self-reported WC and WSR in girls. Due to the media hype around female body shape, girls may be more susceptible to body image distortions, which may partly explain their lower AUC for overweight/obesity than boys. Previous studies have shown that weight misperceptions were more common in girls than boys
Moreover, compared with self-reported WC and WSR, CBS has the advantage of visualising adiposity of the whole body. Adolescents may not know their WC well as it is seldom measured in schools or at home
In girls, these cutoffs were more specific than they were sensitive in detecting overweight/obesity or underweight, which again suggested overestimation of CBS in some girls. LR+ is often used in the clinical setting to evaluate the usefulness of diagnostic tests
In general, our CBS cutoffs are similar to those of previous research
The prevalence rates of underweight and overweight/obesity based on the CBS cutoffs were markedly higher than those based on the International Obesity Task Force standard, suggesting that CBS is sensitive in detecting underweight and overweight/obesity for screening purposes. Screened positive adolescents should then be examined objectively to determine weight status. Early intervention could be implemented when needed, thus preventing long-term psychosocial and health consequences.
Although the performance of CBS was lower than self-reported BMI, CBS can be particularly useful when height and weight are not well recalled, especially in young children and adolescents who may have difficulty reporting their anthropometric data or when participants are reluctant to reveal
The strengths of the present study are the large, representative sample and the inclusion of four different anthropometric indicators for comparison. However, the use of measured BMI as a surrogate measure for general adiposity is a limitation
The third and the fifth Stunkard’s figure drawings were identified as the CBS cutoffs for underweight and overweight/obesity, respectively, in Chinese adolescent boys and girls aged 12–17. CBS is a potentially useful indicator to assess weight status of adolescents when measured and self-reported BMI are not available. The use of CBS to assess the weight status of oneself and others warrants further investigations in different ethnic and age groups.
We would like to thank the schools and students for their participation.