The impact of non-response bias due to sampling in public health studies: A comparison of voluntary versus mandatory recruitment in a Dutch national survey on adolescent health

Table 2 Univariate and multivariable logistic regression analyses

		Univariate model		Multivariable model
	n	OR (95% CI)	Wald	OR (95% CI)	Wald
School experiences^a	11,267	.54 (.50–.58)^*	324.36	.62 (.57–.67)^*	151.51
Subjective health^b	11,248	.80 (.74–.86)^*	37.10	.84 (.77–.91)^*	16.75
SDQ	11,225
Unlikely ^(ref)	9987	1.00	14.31	1.00	9.78
Possible	857	.67 (.54–.83)^*	14.02	.68 (.53–.86)^*	9.77
Probable	381	.90 (.68–1.20)	.50	1.00 (.72–1.38)	.00
Tobacco consumption^c	11,242	.37 (.28–.47)^*	62.22	.45 (.33–.60)^*	30.08
Alcohol consumption^d	10,959	.33 (.30–.37)^*	392.98	.32 (.27–.36)^*	248.80
Lifetime alcohol consumption^e	10,964	.84 (.83–.85)^*	488.22	.81 (.80–83)^*	388.29
Alcohol in past four weeks^f	10,950	.18 (.15–.21)^*	466.79	.13 (.11–.16)^*	365.73
Sexual intercourse^g	10,896	.71 (.64–.78)^*	52.12	.76 (.68–.85)^*	24.29

Univariate and multivariable logistic regression analyses, separately conducted for each health-related variable versus sampling method (mandatory sample (Twente) = 0; voluntary sample (IJsselland) = 1). All analyses were first conducted without correction for demographic differences between both samples), and then repeated with gender, age, and education level added to the models as covariates
^a(1) great fun, (2) fun, (3) neutral, (4) not fun, (5) dreadful
^b(1) very good, (2) good, (3) neutral, (4) not good, (5) poor
^cDaily smoker: (0) no, (1) yes
^dHad ever consumed alcohol: (0) no, (1) yes
^eLifetime alcohol consumption: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11–19, 20 > times
^fHad alcohol in the past four weeks: (0) no, (1) yes
^g(1) never, (2) once, (3) couple of times, (4) regularly
^*= p < .01 (two-tailed)

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