Table 1.

Characteristics of the self-referred patients ( n   = 436)

		Percentage	Number	p value a
Gender	Male	58	251	<0.01
	Female	42	185
Age categories (years)	18 to 35	54	234	<0.01
	35 to 65	40	173
	65+	7	29
Residence	Inner city	70	305	<0.01
	Urban area	21	90
	Netherlands, outside urban study area	6	27
	Abroad	3	14
Nationality	Dutch	67	290	<0.01
	Other	33	146
Level of education	Low or intermediate	73	315	<0.01
	High	27	116
Civil status	Single, no children	42	182	<0.01
	Partner with children	24	105
	Single with children	18	77
	Partner, no children	12	53
	Other	4	17
Shift	Day	45	198	<0.01
	Evening	35	153
	Night	20	85

^aChi-square test.