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 1 Descriptive statistics per sample

	n	Mean (SD)	% of sample		n	Mean (SD)	% of sample
Mandatory sample (Twente)				Voluntary sample (IJsselland)
Age	8761	14.23 (1.14)	-	Age	1571	14.29 (1.07)	-
Education^a	9295	-	51.5	Education^a	1723	-	61.3
Gender^b	9359	-	49.2	Gender^b	1952	-	55.8
School experiences^c	9354	2.52 (.85)	-	School experiences^c	1913	2.13 (.73)	-
Subjective health^d	9356	1.85 (.70)	-	Subjective health^d	1892	1.75 (.69)	-
SDQ	9349	-	-	SDQ	1952	-	-
Unlikely	8275	-	88.5	Unlikely	1712	-	91.3
Possible	753	-	8.1	Possible	104	-	5.5
Probable	321	-	3.4	Probable	60	-	3.2
Tobacco consumption^e	9291	-	9.13	Tobacco consumption^e	1951	-	3.5
Alcohol consumption^f	9015	-	51.8	Alcohol consumption^f	1944	-	26.2
Lifetime alcohol consumption^g	9280	5.67 (5.26)	-	Lifetime alcohol consumption^g	1684	2.31 (3.48)	-
Alcohol in past four weeks^h	9272	-	41.5	Alcohol in past four weeks^h	1678	-	11.1
Sexual intercourseⁱ	9247	1.28 (.79)	-	Sexual intercourseⁱ	1649	1.13 (.55)	-

ISSN: 1471-2458