Table 2.

Association between time and both health-related quality of life and psychosocial problems tested in generalized estimating equations (GEE) models

	Health-related quality of lifea			Psychosocial problemsa,b
	Coefficient	95% CI		Coefficient	95% CI
		Lower limit	Upper limit		Lower limit	Upper limit
Timec
1	Ref	Ref	Ref	Ref	Ref	Ref
2	1.68	0.04	3.31	− 0.05	− 1.21	1.12
3	2.05	0.66	3.44	− 0.15	− 1.18	0.87
4	3.04	1.24	4.84	− 1.33	− 2.50	− 0.17
5	− 0.10	− 1.83	1.63	−	−	−
Sex
Boys	Ref	Ref	Ref	Ref	Ref	Ref
Girls	0.11	− 1.54	1.76	− 0.75	− 1.89	0.39
Age	− 0.28	− 2.08	1.53	− 0.06	− 1.17	1.06
SES	0.40	− 0.12	0.92	− 0.61	− 0.99	− 0.23
Ethnic background
Dutch	Ref	Ref	Ref	Ref	Ref	Ref
Western	− 4.90	− 9.47	− 0.32	− 0.30	− 3.52	2.93
Non− Western	− 0.03	− 2.44	2.38	− 1.88	− 3.38	− 0.38
Grade
5	Ref	Ref	Ref	−	−	−
6	2.33	− 0.02	4.69	–	–	–
7	4.88	0.84	8.93	Ref	Ref	Ref
8	4.14	− 1.48	9.76	− 0.64	− 2.09	0.82

In these models, school was additionally included as a categorical covariate, but the school-specific estimates are not shown

SES = socio-economic status; CI = confidence interval

^aHigher scores indicate higher quality of life and more psychosocial problems

^bPsychosocial problems were only measured in grade 7 and 8 (age 9–13 years) and it was not possible to include T5 in the GEE models (comparing T5 with T1 separately: B = 1.18, 95% CI [− 0.20, 2.56])

^cCorresponding to T1–T5, with T1 containing the measurement occasions at both 0 and 4 months