Date: Fri, 6 Jun 2003 16:34:46 -0700 Reply-To: cassell.david@EPAMAIL.EPA.GOV Sender: "SAS(r) Discussion" From: "David L. Cassell" Subject: Re: Again SURVEYSELECT for stratified sampling Comments: To: SASKID Content-type: text/plain; charset=us-ascii SASKID wrote: > Original message was: "It's getting closer. Which SURVEYSELECT method > would you recommend if you wanted a stratified sample from a finite > population in such a way that the sample keeps all the strata > proportions of the population? Maybe PPS? For example, if the population > has N=1000, and male/female are50%/50%, and big/small 80%20%, which > sampling method could you recommend to reach at at sample of, say, > N=100, and male/female are50%/50%, and big/small 80%20%, too? Perhaps I do not grasp all of what you are tryingto accomplish, but if you want the proportions in the sample to mimic those in the population, just take a simple random sample. That would be METHOD=SRS . Of course, you will not get *exactly* the numbers you want when you do simple random sampling. If you need exact numbers (for some unspecified reason), then you could make your four categories (male or female, big or small) into four strata. Then sample each of your four strata at 10%, to get much closer to the exact proportions in your population. Still, unless the counts in these strata are multiples of ten, you are not going to get *exactly* one-tenth. Assume you performed a PROC FREQ and found that the four categories look like this: stratum male/female big/small count 1 M B 131 2 M S 582 3 F B 198 4 F S 89 Now you need to create a stratum variable with exactly the above numbers, and name it something, perhaps STRAT1. Then you could specify your stratum sizes for your sample using something like this: proc sort data=YourFrame; by strat1; run; proc surveyselect data=YourFrame out=YourSample sampsize=(13,58,20,9) method=srs seed=193756345; id ; strata strat1; run; Note that the stratum sizes will be chosen *in* *order*, so sort the frame data by the stratum, and make sure the stratum numbers match up with the strata. Choose your own random seed, too. HTH, David -- David Cassell, CSC Cassell.David@epa.gov Senior computing specialist mathematical statistician

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