Odds Ratio	95% Confidence Interval	p-value
Invitation mode
Paper only	Ref	--	--
Web only1	6.96	6.01, 8.07	<0.0001
Both paper and web2	2.27	2.13, 2.43	<0.0001
Gender
Male	1.09	1.02, 1.17	0.013
Female	Ref	--	--
Race/ethnicity
White non-Hispanic	Ref	--	--
Black non-Hispanic	0.74	0.67, 0.82	<0.0001
Hispanic	0.91	0.82, 1.01	0.076
Asian	0.84	0.71, 1.00	0.048
Multiple races	1.02	0.81, 1.27	0.884
Other	0.80	0.59, 1.10	0.165
Age group
28–49 years	Ref	--	--
50–59 years	1.43	1.27, 1.60	<0.0001
60–64 years	1.82	1.63, 2.04	<0.0001
65+ years	1.91	1.72, 2.13	<0.0001
Household income
Less than $25,000	0.79	0.68, 0.93	0.004
$25,000 – < $50,000	0.94	0.83, 1.06	0.319
$50,000– <$75,000	1.01	0.90, 1.13	0.844
$75,000 – <$150,000	1.14	1.03, 1.26	0.011
$150,000 or more	Ref	--	--
Marital status
Married or living with partner	Ref	--	--
Divorced or separated	0.97	0.88, 1.06	0.466
Widowed	0.97	0.79, 1.18	0.758
Never married	0.98	0.89, 1.07	0.605
Educational attainment
High school or less	0.96	0.87, 1.06	0.384
Some college	0.92	0.84, 1.01	0.079
Bachelor's degree	1.00	0.91, 1.09	0.915
Postgraduate degree	Ref	--	--
Eligibility group
Rescue/recovery worker	Ref	--	--
Resident	0.67	0.60, 0.74	<0.0001
Area worker, student/school staff	1.02	0.95, 1.10	0.534
Passer-by	0.88	0.76, 1.03	0.101