The final sample consisted o f 1177 girls. The sample were divided between two school year groups, such that 582 were in school year 9 and 595 in school year
10.
4.4.1 Demographic Characteristics of the Sample
The mean age of participants is shown in Table 4.12 and other demographic charactristics of the sample, including ethnicity and socioeconomic status, is shown in table 4.13. Participants were all aged between 12 and 16 years at baseline. Although all participants were in school years 9 and 10, a small number of individuals were outside the usual age range for these year groups, and they account for the wide range of ages. The vast majority of those in the sample (97.8%) were aged between 13 years 1 month and 15 years 6 months. Participants were divided evenly between the two year-groups, and just over half attended single sex girls’ schools.
Table 4.12 Mean (SD) and range of age in the sample
Age Mean 14y 5m (SD) (8m) Max 15y 9m Min 12y 9m 4.4.1.1 Ethnicitv
The overwhelming majority of the participants (92%) identified themselves as white. The full breakdown o f ethnic origin can be seen in table 4.13. Due to the lack of variation, no analyses based on ethnicity were carried out.
Chapter 4. Baseline methodology and descriptive statistics
Table 4.13 Demographic composition of sample
% (n) School Year Year 9 49.4 (582) Year 10 50.6 (595) School Type Girls 54.0 (636) Mixed sex 46.0 (541) Ethnicity White 92.3 (1086) Black 0.8 (9) Asian 0.6 (7) Mixed Race 4.6 (54) Other 0.9 (11) Missing 0.8 (10) Family Composition
Living with Mother 93.9 (1105)
Living with Father 77.1 (907)
Socioeconomic status
Eligible for free school meals 31.6 (372)
Social Class I 11.4 (134) II 29.8 (351) Illnm 10.8 (127) Him 15.8 (186) IV 5.7 (67) V 2.7 (32) Unclassified 2T 8 (280)
Car ownership No car 9.5 (112)
One car 43.4 (512)
2 or more cars 46.4 (546)
Missing 0.6 (7)
Housing tenure Privately owned 73.5 (865)
Rented 18.6 (219)
Chapter 4. Baseline methodology and descriptive statistics
4.4.1.2 Socioeconomic status
The selection o f schools for the sample ensured that participants were taken from a wide range o f social and economic backgrounds, and the data confirms that they were spread across the social classes, based on the highest social class indicated by their mother's or father's occupation. The large majority o f participants lived with a mother or stepmother, and around three-quarters with a father or stepfather. It was possible to code just over three quarters of participants for social class. Unclassified responses include families where neither parent is in employment. Just under one third of pupils claimed to be eligible to receive school meals, indicating a level of deprivation equivalent to the receipt of income support. One in five participants in the sample lived in rented accommodation, whilst one in ten had no access to a family car.
4.4.2 Anthropometries, body dissatisfaction and dieting
4.4.2.1 BMI, Height and Weight
Mean height, weight and body mass index of the two year groups is indicated in table 4.12. As expected the older girls were on average taller (t[df=l 156]=6.25 p<0.001), heavier (t[df=l 133]=4.34 p<0.001) and had a higher BMI (t[df=l 133]=2.51 p<0.05) than the younger girls.
Around half o f participants reported being Satisfied or very satisfied with their body weight. Two thirds of the sample had tried to control their weight in the past, and half reported dieting in the past year. There were no significant differences between the two age groups for body dissatisfaction (x^[df=l]=1.07 ns), weight control (x^[df=l]=1.91 ns) or dieting (x^[df=l]=1.93 ns).
Chapter 4. Baseline methodology and descriptive statistics
Table 4.14 Descriptive statistics for weight, height, body dissatisfaction and dieting by year group.
Year 9 (N=582) Year 10 (N=595) Total (N= 1177) Height (cm) Mean 160 (64) 162 (60) 161(63) Max 182 182 182 Min 140 145 140 Weight (kg) Mean (SD) 54.7(11.4) 57.5 (10.2) 56.1 (10.9) Max 116.8 100 116.8 Min 28.4 33.9 28.4
Body Mass Index
Mean (SD) 21.3 (3.8) 21.9 (3.6) 21.6(3.7) Max 3&6 41.4 41.4 Min 14.4 15.2 14.4 Body Dissatisfaction %(n) Very satisfied 11.3 (66) 10.6(63) 11.0(129) Satisfied 41.6(242) 38.8 (231) 40.2 (473) Dissatisfied 31.8(185) 34.8 (207) 33.3 (392) Very dissatisfied 14.6(85) 14.1 (84) 14.4(169) Missing 0.7 (4) 1.7(10) 1.2(14)
Ever attempted weight control %(n) 64.9 (378) 68.7 (409) 66.9 (787) Dieting in the past year 55.2 (321) 59.2 (352) 57.2 (673)
4.4.3 Weight status and weight perceptions
4.4.3.1 Weight status
The prevalence o f underweight, overweight and obesity is indicated in table 4.15. According to this method of calculating weight status, which takes into account normal age-related changes in BMI (Cole et al, 2000), there were no significant differences in levels of overweight and obesity between the two age groups (x^[df=2]=0.63 ns). The younger girls were, however, somewhat more likely to be underweight for their age than the older girls (x^[df=l]=10.6 p<0.01).
Chapter 4. Baseline methodology and descriptive statistics
Table 4.15 Weight status by school year (Based on age adjusted norms)
Year 9 (N=582) Year 10 (N=595) Total (N= 1177)
% (n) % (n) % (n) Underweight 5.2 (30) 2.2 (13) 3.7 (43) Normal 68.4 (398) 69.7 (415) 69.1 (813) Overweight* 18.6 (108) 18.7 (111) 18.6 (219) Obese 5.7 (33) 4.5 (27) 5.1 (60) Missing 2.2 (13) 4.9 (29) 3.6 (42)
* Overweight category does not include the obese
4.4.3.2 Weight perceptions
The extent to which adolescents in the sample accurately described their own weight status is indicated in table 4.16. The two perceived underweight categories were collapsed due to low levels of endorsement o f these categories.
Table 4.16 Accuracy of weight perceptions
N = 1122 Perceived weight status % (n)
Actual weight status Too thin About right A bit too fat Much too fat
Underweight ^ f ( 2 6 ) 3 2 .6(14) 7 .0 (3 )
Normal weight n 6 (92) 53.8 (437) 30.3 (246) 3.4 (28)
Overweight - 14.6 (32) 63.0(138) 21.9(48)
Obese - 5 .0 (3 ) 50.0 (30) 4 1 .7(25)
The majority of underweight girls perceived themselves to be too thin, with only a very few feeling that they were too fat. Most normal weight girls placed themselves in the 'about right' category, although around one in three felt they were a bit too fat and a small percentage felt themselves to be much too fat. The large majority of overweight and obese girls correctly identified themselves as too fat.
Chapter 4. Baseline methodology and descriptive statistics