Stat Computing > SAS > FAQ

SAS FAQ 
How do I analyze survey data with a two-stage cluster with unequal probabilities design?

This example is taken from Levy and Lemeshow's Sampling of Populations.

page 350 cluster sampling with unequal probabilities:  probability proportional to size sampling
This example uses the hospslect data set.

proc surveymeans data = hospslct n = 4672 sum mean;
  weight wstar;
  cluster drawing;
  var lifethrt dxdead;
run;

The SURVEYMEANS Procedure

            Data Summary

Number of Clusters                 5
Number of Observations            50
Sum of Weights                 50056

                               Statistics

                               Std Error
Variable            Mean         of Mean             Sum         Std Dev
------------------------------------------------------------------------
LIFETHRT        0.120000        0.019989     6006.720000     1000.584155
DXDEAD          0.040000        0.024482     2002.240000     1225.460312
------------------------------------------------------------------------

Page 353 cluster sampling with unequal probabilities:   probability proportional to size sampling

data hspslct2;
  set hospslct;
  /*n is 50*/
  /*N_i is admiss*/
  /* X is 7087, the total number of life-threating conditions across all the hospitals*/
  /*X_i is tl, the total number of life-threating conditions for each hospital*/
  if hospno = 2 then  tl = 785; 
  if hospno = 5 then  tl = 3404; 
  if hospno = 9 then  tl = 778; 
  w2star = (admiss/50)*(7087/tl);
run;

proc surveymeans data = hspslct2 n = 4672 mean sum;
  weight w2star;
  cluster drawing;
  var lifethrt dxdead;
run;

The SURVEYMEANS Procedure

            Data Summary

Number of Clusters                 5
Number of Observations            50
Sum of Weights            51344.9973

                               Statistics

                               Std Error
Variable            Mean         of Mean             Sum         Std Dev
------------------------------------------------------------------------
LIFETHRT        0.121904        0.021404     6259.175814     1276.638273
DXDEAD          0.034287        0.022991     1760.471466     1078.465840
------------------------------------------------------------------------

UCLA Researchers are invited to our Statistical Consulting Services
We recommend others to our list of Other Resources for Statistical Computing Help
These pages are Copyrighted (c) by UCLA Academic Technology Services