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

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

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  
  1. ** 95%Cl = 95% confidence interval
  2. † p value from likelihood ratio test statistic comparing models with and without the listed categories of the specified factor
  3. Eleven studies were excluded because they did not report the number of reminders.
  4. Odds ratios above 1.0 indicate a higher response rate in that category than in the reference group.