Table 2.

Demographic characteristics of patient sample by level of study participation with P value for tests of variation across the three groups

	Patients sent but not returning a test questionnaire within 3 weeks of mail out.a	Patients sent but not returning a retest questionnaire within 4 weeks of mail out.	Patients returning both a test and a retest questionnaire within the deadlines.	P value
Number	2009	249	348	n/a
Number (%) male	807 (40.1)	89 (35.7)	138 (39.7)	0.404
Number (%) white Britisha	404 (88.0)	204 (89.1)	326 (95.6)	0.001
Mean (SD) age in years	46.2 (18.5)	59.4 (18.8)	65.3 (15.1)	<0.001

^aEthnicity data was only available for those who returned a completed test questionnaire and responded to the ethnicity item. For patients sent but not returning a test questionnaire within 3 weeks of mail out, n = 473; for patients sent but not returning a retest questionnaire within 4 weeks of mail out, n = 229; for patients returning both a test and a retest questionnaire within the deadlines, n = 341