Response rates in postal surveys of healthcare professionals between 1996 and 2005: An observational study

Table 3 Odds ratios (ORs) from final multivariable multilevel model

Categories	Number of:		Odds ratio
	Studies	Participants	OR	95%Cl**	p†
Country					< 0.0001
US, Canada, Australia, New Zealand	178	222,016	1.00	-
All other countries	161	128,325	1.34	1.13 to 1.60
Number of reminders					0.0009
None	176	176,886	1.00
One or more	163	173,455	1.33	1.13 to 1.57
Number of survey participants					< 0.0001
> = 1,000	92	252,428	1.00	-
500-999	80	53,345	1.30	1.03 to 1.63
<500	167	44,568	1.97	1.61 to 2.41
Length					0.0008
Length reported	234	255,802	1.00	-
Length not reported	105	94,539	1.37	1.14 to 1.64

** 95%Cl = 95% confidence interval
† p value from likelihood ratio test statistic comparing models with and without the listed categories of the specified factor
Eleven studies were excluded because they did not report the number of reminders.
Odds ratios above 1.0 indicate a higher response rate in that category than in the reference group.