How many mailouts? Could attempts to increase the response rate in the Iraq war cohort study be counterproductive?

Table 1 Response rates according to demographic and other factors. Response differed significantly for all factors shown ((p < 0.001)

		Total N	Percentage (weighted) who responded
Age (years) at 01/01/05	<25	3,442	50
	25–29	3,347	58
	30–34	3,432	64
	35–39	3,173	67
	40–49	3,137	64
	50–60	631	69
Gender	Male	15,585	60
	Female	1,577	67
Service	Naval Service	2,943	57
	Army	10,936	61
	RAF	3,283	61
Rank	Officer	2,718	70
	Rank	14,444	59
Status	Reservist	2,987	53
	Regular	14,175	61
Deployment	Era	9,627	58
	TELIC 1	7,535	63
Ethnic group*	White	14,142	62
	Non-white	882	56
All addresses military	Yes	12,705	70
	No	4,457	30
Military unit visited	Yes	5,252	68
	No	11,910	57
	Total	17,162	60

ISSN: 1471-2288