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.

Cook et al. BMC Health Services Research 2009 9:160   doi:10.1186/1472-6963-9-160