The average BMI Z-score of the sample was 2.45 ± 0.46, with 212 participants classified as obese (88%) and 29 (12%) considered overweight. For a more detailed description of the sample characteristics, see Tables 1 and 2.
Table 1
Descriptive sample characteristics
Categoric variables
|
N
|
%
|
Sex
Female
Male
Migration Background
Yes/German
No/Non-German
Percentile
Obese
Overweight
Parent’s Educational Degree*
High
|
125
116
209
32
212
29
57
|
51.9
48.1
13.3
86.7
88.0
12.0
23.7
|
Low
|
184
|
76.3
|
*High, both parents have completed secondary school;
Low, only one parent/ neither mother nor father have completed secondary school
|
Table 2
Descriptive sample characteristics
Continuous variables
|
N
|
Mean (SD)
|
Min
|
Max
|
Physical variables
|
|
|
|
|
Age (years)
|
241
|
12.5 (2.07)
|
7.3
|
17.1
|
Height (m)
|
241
|
1.58 (0.11)
|
1.23
|
1.89
|
Weight (kg)
|
241
|
76.7 (19.9)
|
37.4
|
148.4
|
BMI (kg/m2)
|
241
|
30.9 (4.8)
|
20.5
|
56.6
|
BMI Z-score
|
241
|
2.45 (0.46)
|
1.43
|
3.80
|
Body fat (%)
|
241
|
42.1 (9.0)
|
26.1
|
83.2
|
Relative Physical fitness (W/kg)
|
238
|
1.7 (0.4)
|
0.9
|
3.3
|
Lifestyle variables
|
|
|
|
|
Physical Activity (hours/week)
|
162
|
5.1 (4.1)
|
0
|
20.0
|
Media Consumption (hours/week)
|
190
|
17.2 (12.4)
|
0
|
59.5
|
Psychosocial variables
|
|
|
|
|
HRQOL
|
232
|
77.7 (14.3)
|
29.1
|
100.0
|
Scholastic Competence
|
233
|
75.6 (16.7)
|
25.0
|
100.0
|
Social Competence
|
232
|
76.0 (18.6)
|
25.0
|
100.0
|
Physical Appearance
|
233
|
54.1 (15.6)
|
25.0
|
100.0
|
Behavioral Conduct
|
233
|
74.1 (16.4)
|
29.2
|
100.0
|
Global Self-Worth
|
233
|
72.3 (16.3)
|
25.0
|
100.0
|
HRQOL, Health-Related Quality of Life; SD, Standard Deviation; Min, Minimum; Max, Maximum; Psychosocial variables are based on scores ranging from 0 (lowest) to 100 (highest)
|
Table 3 presents the six baseline multivariable linear regression models explaining HRQOL and the dimensions of self-concept, ie, scholastic competence, social competence, physical appearance, behavioral conduct, and global self-worth, adjusting for all independent variables. Table 4 summarizes the resulting final models after using backward stepwise multivariable regression analysis.
Table 3
Baseline Multivariable Linear Regression Models
Variables
Coef ± s.e.
(P-value)
|
HRQOL
|
Scholastic Competence°
|
Social Competence°
|
Physical Appearance°
|
Behavioral Conduct°
|
Global Self-Worth°
|
N
|
136
|
136
|
136
|
136
|
136
|
136
|
Age (years)
|
-3.755 ± 6.458 (0.562)
|
-5.039 ± 7.192
(0.485)
|
-4.942 ± 8.267 (0.551)
|
-0.8249 ± 6.834 (0.223)
|
-6.175 ± 0.7508 (0.412)
|
-12.603 ± 7.705 (0.104)
|
Age squared (years)
|
0.160 ± 0.264 (0.546)
|
0.157 ± 0.291 (0.590)
|
0.189 ± 0.335 (0.574)
|
0.247 ± 0.277 (0.327)
|
0.210 ± 0.304 (0.492)
|
0.448 ± 0.312 (0.153)
|
Femalea
|
-4.300 ± 2.533 (0.092)
|
-2.779 ± 2.789 (0.321)
|
3.062 ± 3.205 (0.341)
|
-2.606 ± 2.650 (0.327)
|
-1.593 ± 2.911 (0.663)
|
-0.822 ± 2.987 (0.787)
|
BMI Z-score
|
-2.457 ± 3.585 (0.495)
|
0.590 ± 3.884 (0.880)
|
8.360 ± 4.465 (0.064)
|
-10.031 ± 3.691 (0.008)
|
4.845 ± 4.055 (0.234)
|
-4.678 ± 4.161 (0.263)
|
Body Fat (%)
|
-0.223 ± 0.159 (0.164)
|
-0.005 ± 0.176 (0.978)
|
-0.342 ± 0.202 (0.093)
|
-0.163 ± 0.167 (0.332)
|
-0.215 ± 0.184 (0.244)
|
-0.049 ± 0.188 (0.795)
|
High Parental Educational Levelb
|
3.692 ± 2.906 (0.206)
|
6.471 ± 3.098 (0.039)
|
3.198 ± 3.561 (0.371)
|
0.031 ± 2.944 (0.992)
|
6.814 ± 3.234 (0.037)
|
6.898 ± 3.319 (0.040)
|
German/No Migration Backgroundc
|
-3.170 ± 4.054 (0.436)
|
3.135 ± 4.373 (0.475)
|
-2.500 ± 5.027 (0.620)
|
-3.281 ± 4.155 (0.431)
|
8.332 ± 4.565 (0.070)
|
1.018 ± 4.685 (0.828)
|
Relative Physical Fitness (W/kg)
|
4.736 ± 3.750 (0.209)
|
7.769 ± 4.012 (0.055)
|
8.804 ± 4.612 (0.059)
|
-1.622 ± 3.812 (0.671)
|
5.485 ± 4.189 (0.193)
|
1.416 ± 4.298 (0.742)
|
Physical Activity (hours)
|
-0.309 ± 0.318 (0.334)
|
0.217 ± 0.341 (0.526)
|
0.278 ± 0.392 (0.479)
|
-0.691 ± 0.324 (0.035)
|
-0.156 ± 0.356 (0.663)
|
-0.192 ± 0.365 (0.601)
|
Media Consumption (hours)
|
-0.128 ± 0.103 (0.220)
|
0.012 ± 0.109 (0.910)
|
-0.171 ± 0.126 (0.177)
|
-0.146 ± 0.104 (0.164)
|
-0.120 ± 0.114 (0.297)
|
-0.028 ± 0.117 (0.811)
|
R2
|
0.134 (0.045)
|
0.114 (0.113)
|
0.103 (0.175)
|
0.218 (< 0.001)
|
0.122 (0.078)
|
0.114 (0.111)
|
Adj. R2
|
0.065 (0.045)
|
0.043 (0.113)
|
0.031 (0.175)
|
0.156 (< 0.001)
|
0.052 (0.078)
|
0.043 (0.111)
|
HRQOL, Health-Related Quality of Life; Coef, β-Regression Coefficient; s.e., Standard Error; Adj, Adjusted |
°Subdomains of self-concept |
Reference Categories: a Male, b low parental educational level (only one parent/neither mother nor father have Abitur), c Non-German |
Table 4
Final Models from Backward Stepwise Multivariable Linear Regression Analysis*
Variables
Coef ± s.e.
(P-value)
|
HRQOL
|
Scholastic Competence°
|
Social Competence°
|
Physical Appearance°
|
Behavioral Conduct°
|
Global Self-Worth°
|
N
|
136
|
136
|
136
|
136
|
136
|
136
|
Age (years)
|
|
|
|
-0.245 ± 0.641 (0.001)
|
|
-1.599 ± 0.719 (0.028)
|
Age squared (years)
|
|
|
|
|
|
|
Femalea
|
|
|
|
|
|
|
BMI Z-score
|
|
|
|
-11.557 ± 2.726 (< 0.001)
|
|
|
Body Fat (%)
|
|
|
|
|
|
|
High Parental Educational Levelb
|
|
|
|
|
7.165 ± 2.942 (0.016)
|
8.034 ± 3.005 (0.008)
|
German/No Migration Backgroundc
|
|
|
|
|
8.983 ± 4.442 (0.045)
|
|
Relative Physical Fitness (W/kg)
|
8.024 ± 3.128 (0.011)
|
8.916 ± 3.289 (0.008)
|
8.678 ± 3.786 (0.023)
|
|
|
|
Physical Activity (hours)
|
|
|
|
-0.623 ± 0.301 (0.040)
|
|
|
Media Consumption (hours)
|
|
|
|
|
|
|
R2
|
0.047 (0.011)
|
0.052 (0.008)
|
0.038 (0.023)
|
0.190 (< 0.001)
|
0.071 (0.008)
|
0.077 (0.005)
|
Adj. R2
|
0.040 (0.011)
|
0.045 (0.008)
|
0.031 (0.023)
|
0.171 (< 0.001)
|
0.057 (0.008)
|
0.063 (0.005)
|
*After excluding all insignificant variables. Significance was set at P < 0.05 |
HRQOL, Health-Related Quality of Life; Coef, β-Regression Coefficient; s.e., Standard Error; Adj, Adjusted |
°Subdomains of self-concept |
Reference Categories: a Male, b low parental educational level (only one/neither mother nor father have Abitur), c Non-German |
After all other factors had been accounted for in the final models explaining HRQOL, scholastic competence, and social competence, relative physical fitness remained the only significant predictor. Participants with high levels of relative physical fitness (W/kg) showed higher HRQOL (β = 8.024 ± 3.1283, P = 0.011; R2 = 0.040, P = 0.011) and perceived scholastic (β = 8.9162 ± 3.289, P = 0.008; R2 = 0.045, P = 0.008) and social competence (β = 8.6878 ± 3.7986, P = 0.023; R2 = 0.031, P = 0.023). While relative physical fitness explained approximately 3.1–4.75% of total variability in each of the first three models, it showed no significant association with the other domains of self-concept.
BMI Z-score, demographic variables, and lifestyle variables, were not significant predictors of HRQOL or social and scholastic competence. We found BMI Z-score and physical activity to be significantly associated with only one of the dependent variables investigated. More precisely, BMI Z-score (β=−11.557 ± 2.726, P < 0.001) and self-reported physical activity (β=−0.623 ± 0.301, P = 0.040) significantly predicted physical appearance. Jointly with age (β=−0.245 ± 0.641, P = 0.001), the three predictors accounted for approximately 17% of the total variability in the final physical appearance model (R2 = 0.171, P < 0.001), which showed no further significant associations with the other observed predictors.
Concerning the first four regression models, predictors of parental educational background and migration background were not significant. In the fifth model explaining behavioral conduct, however, parents’ educational background (β = 7.165 ± 2.942, P = 0.016) and migration background (β = 8.983 ± 4.442, P = 0.045) explained a significant proportion of variance (R2 = 0.057, P = 0.008), indicating that children and adolescents with obesity and overweight who have a migration background or whose parents had comparatively low education assessed their behavioral conduct as worse than their German counterparts. Higher parental education was also positively associated with global self-worth (β = 8.034 ± 3.005, P = 0.008), and together with age (β=−1.599 ± 0.719, P = 0.028) accounted for approximately 6% of total variability in the final global self-worth model (R2 = 0.063, P = 0.005). We were unable to find further significant predictors in the behavioral conduct and global self-worth models. Sex, body fat, age squared and media consumption were not significant predictors in any of the final regression models.