Effectiveness of incentives and follow-up on increasing survey response rates and participation in field studies

Table 2 Results of the regression models for recipients completing the survey (including only deliverable surveys)

Model and test relative to intercept-only model	Variable	Fixed effects			Variable level	Completing survey
Model and test relative to intercept-only model	Variable	df	Wald χ²	p-value	Variable level	p-value	OR	95% CI
Model 1 χ²(6, n = 3576) = 158.793, p < 0.0001	Survey incentive	1	11.599	< 0.001	Gift card	Ref
					$2	< 0.001	2.792	1.546–5.041
	Survey length	2	2.569	0.277	Short	Ref
					Medium	0.752	0.927	0.579–1.484
					Long	0.139	0.730	0.482–1.107
	Follow-up waves	2	9.627	0.008	0	Ref
					2	0.114	1.530	0.903–2.591
					3	0.005	2.121	1.250–3.597
	Field study incentive	1	0.150	0.699	150	Ref
					200	0.699	0.936	0.671–1.306
Model 2 χ²(11, n = 3576) = 162.574, p < 0.0001	Survey incentive	1	11.643	< 0.001	Gift card	Ref
					$2	< 0.001	2.798	1.550–5.054
	Survey length	2	2.505	0.286	Short	Ref
					Medium	0.759	0.929	0.580–1.488
					Long	0.144	0.733	0.483–1.112
	Follow-up waves	2	9.592	0.008	0	Ref
					2	0.114	1.530	0.903–2.592
					3	0.005	2.120	1.249–3.596
	Field study incentive	1	0.170	0.680	150	Ref
					200	0.680	0.932	0.668–1.301
	Noise exposure category	4	3.397	0.494	< 40	Ref
					40–45	0.562	0.907	0.651–1.263
					45–50	0.306	0.839	0.599–1.175
					50–55	0.671	1.073	0.776–1.484
					> 55	0.594	1.093	0.787–1.519
	Direction	1	1.073	0.300	West	Ref
					East	0.538	0.936	0.758–1.156

All analyses excluded surveys that could not be delivered for any reason
df Degrees of freedom, OR Odds Ratio, CI Confidence Interval, Ref Reference category
Statistically significant (p < 0.05) results are indicated with bold typeface

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