Task 1c: How to Estimate a Mean Ratio using SUDAAN

This section describes how to use SUDAAN to estimate a mean ratio for all adults and for males and females separately.  To illustrate this, the sum of calcium from milk is divided by the sum of total calcium for each population group as an example.

 

Step 1: Sort Data

This section describes how to use SUDAAN and SAS to estimate mean ratios for all adults and for males and females separately.  The illustrate this, the calcium from milk is divided by the sum of total calcium for each person and these ratios are averaged for each group as an example.

Sort the data by strata and PSU.  Data must always be sorted first when using SUDAAN. In the sample code below, DTTOT is the dataset that was created for this analysis with the appropriate variables of interest.

For this analysis, DAY1RATIO is a variable that was created to represent the ratio of the amount of calcium from milk to the amount of total calcium for each individual on recall Day 1.

 

Step 2: Compute Properly Weighted Estimated Mean Ratios

Use SUDAAN to Estimate Mean Contribution of Milk to Calcium Intake for All Adults, Males, and Females, Ages 20 Years and Older

Sample Code

*-------------------------------------------------------------------------;
* Use the PROC SORT procedure to sort the data by strata and PSU.         ;
*-------------------------------------------------------------------------;

proc sort data =DTTOT;
      by SDMVSTRA SDMVPSU;
run ;

*-------------------------------------------------------------------------;
* Use the PROC DESCRIPT procedure in SUDAAN to compute a properly weighted;
* estimated mean ratio for all persons ages 20+.                          ;
*-------------------------------------------------------------------------;

proc descript data =DTTOT;
      setenv decwidth=5 colwidth= 20 ;
      nest SDMVSTRA SDMVPSU;
      weight WTDRD1;
      subgroup RIAGENDR;
      levels 2 ;
      var DAY1RATIO;
      tables RIAGENDR;
      subpopn usedat= 1 /name= "Age 20+ with reliable Day1 recall" ;
      rtitle "Mean Ratios" ;
run ;

 

Output of Program


For Subpopulation: Age 20+ with reliable Day1 recall   
Mean Ratios 
          
Number of observations read    :   9034    Weighted count :286222757
Number of observations skipped :   1088                
(WEIGHT variable nonpositive)                          
Observations in subpopulation  :   4448    Weighted count:205284669 
Denominator degrees of freedom :     15                

Variance Estimation Method: Taylor Series (WR)         
by: Variable, Gender - Adjudicated.                    
            
-----------------------------------------------------------------------------------------------------------
|                 |                  |                                                                    |
| Variable        |                  | Gender - Adjudicated                                               |
|                 |                  | Total                | male                 | female               |
-----------------------------------------------------------------------------------------------------------
|                 |                  |                      |                      |                      |
| DAY1RATIO       | Sample Size      |           4447.00000 |           2134.00000 |           2313.00000 |
|                 | Weighted Size    |      205081760.39614 |       98461101.74649 |      106620658.64965 |
|                 | Total            |       15659108.92268 |        8212141.01881 |        7446967.90388 |
|                 | Lower 95% Limit  |                      |                      |                      |
|                 |  Total           |       11604497.09333 |        6113268.12078 |        5227756.20478 |
|                 | Upper 95% Limit  |                      |                      |                      |
|                 |  Total           |       19713720.75203 |       10311013.91683 |        9666179.60298 |
|                 | Mean             |              0.07636 |              0.08340 |              0.06985 |
|                 | SE Mean          |              0.00469 |              0.00473 |              0.00686 |
|                 | Lower 95% Limit  |                      |                      |                      |
|                 |  Mean            |              0.06635 |              0.07333 |              0.05523 |
|                 | Upper 95% Limit  |                      |                      |                      |
|                 |  Mean            |              0.08636 |              0.09348 |              0.08446 |
----------------------------------------------------------------------------------------------------------

Highlights from the output include:

 

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