New Contributor
Posts: 3

# How Do I Calculate Weighted Confidence Intervals in Proc SurveyFreq

[ Edited ]

Hello everyone. I'm working on analysis of a dataset in SAS 9.3 and have come across a bit of a bump.

I'm analyzing weighted individual-level immunization data to determine statistical differences in two populations. The variable of interest is whether or not the individual is up-to-date for a specific vaccine, which is coded as either a 1 (up-to-date) or 0 (not up-to-date). Each person is coded into groups, like the type of school which the child attends (public=1 versus private=2). I am trying to find out if there are significant differences in vaccination coverage between the two populations using a proc surveyfreq statement. Below is an example of the code I've been running:

proc surveyfreq data = samplecode;
tables schooltype*vaccine /chisq clwt;
weight finalweight;
run;

where schooltype is the type of school which the child attends, vaccine is the vaccine up-to-date status, and finalweight is the calculated weight for each data point. Pretty basic.

Running the proc surveyfreq does give me the significance testing I'm looking for, but I'm stuck on getting the confidence intervals for the weighted percent. The CLWT statement gives me the weighted frequency for each item, but does not really give me the denominator.

I'm confused as to whether or not I should be using the 95% confidence limits for the weighted frequency (red font in the table below) and dividing that by the weighted frequency for the total (blue font in the table below) or if it should be done as a factor of dividing it by the 95% confidence limits for the weighted frequency of the total (green font in the table below), if that makes sense. I have included the output from my proc surveyfreq, if that helps. Or is there a better way to get the weighted confidence interval percentages that I'm not thinking of? I have attached a cutout of the database (samplecode.sas7bdat) I've been using, if what I'm saying isn't making any sense.

 Table of schooltype by vaccine schtype Vaccine Frequency Weighted Frequency Std Dev of Wgt Freq 95% Confidence Limits for Wgt Freq (Lower) 95% Confidence Limits for Wgt Freq (Upper) Percent Std Err of Percent Public 0 473 2692 218.49023 2264 3120 7.2923 0.5724 1 6887 31931 639.46982 30677 33184 86.4912 0.6255 Total 7360 34623 660.26749 33329 35917 93.7835 0.2812 Private 0 41 116.34991 23.42817 70.42485 162.27498 0.3152 0.0637 1 903 2179 92.61625 1997 2360 5.9013 0.2725 Total 944 2295 95.21339 2108 2482 6.2165 0.2812 Total 0 514 2809 219.57097 2378 3239 7.6074 0.5752 1 7790 34109 633.0423 32869 35350 92.3926 0.5752 Total 8304 36918 652.59385 35639 38197 100

Thank you for taking the time to read and please let me know if anything comes to mind.

Super User
Posts: 11,810

## Re: How Do I Calculate Weighted Confidence Intervals in Proc SurveyFreq

Did you try the option CL ?

New Contributor
Posts: 3

## Re: How Do I Calculate Weighted Confidence Intervals in Proc SurveyFreq

Hello and thanks for your input.

Yes, I did try CL as a method, but it only creates confidence limits for the percentage without the weights, as seen below.

 schooltype vaccine Frequency Weighted Frequency Std Dev of Wgt Freq Percent Std Err of Percent 95% Confidence Limits for Percent (Lower) 95% Confidence Limits for Percent (Upper) 0 473 2692 218.49023 7.2923 0.5724 6.1702 8.4144 1 6887 31931 639.46982 86.4912 0.6255 85.2651 87.717 Total 7360 34623 660.26749 93.7835 0.2812 93.2324 94.335 0 41 116.34991 23.42817 0.3152 0.0637 0.1903 0.44 1 903 2179 92.61625 5.9013 0.2725 5.3671 6.4356 Total 944 2295 95.21339 6.2165 0.2812 5.6653 6.7676 Total 0 514 2809 219.57097 7.6074 0.5752 6.4799 8.735 1 7790 34109 633.0423 92.3926 0.5752 91.265 93.52 Total 8304 36918 652.59385 100
Discussion stats
• 2 replies
• 993 views
• 0 likes
• 2 in conversation