Sample 24722: Simple random sample without replacement
Select a random sample where no observation can be
chosen more than once.
Note:
Method 1 uses PROC SURVEYSELECT which is part of the
SAS/STAT package in Version 7 and above. If you have
Version 6 of SAS or do not have SAS/STAT licensed, see
Methods 2 and 3 which use Base SAS.
/* WORK.EASTHIGH is a data base of student grade point averages */
/* from East High School, Grades 9 through 12, 100 or more students per grade. */
data EastHigh;
format GPA 3.1;
do Grade=9 to 12;
do StudentID=1 to 100+int(201*ranuni(432098));
GPA=2.0 + (2.1*ranuni(34280));
output;
end;
end;
run;
/* Method 1: Using PROC SURVEYSELECT */
/* */
/* Use METHOD=SRS. N= is the number of observations to select. */
/* The sample is stored in the OUT= data set, SAMPLE1. */
proc surveyselect data=EastHigh method=srs n=15 out=sample1;
run;
title "Method 1: PROC SURVEYSELECT";
proc print data=sample1;
run;
/* Method 2: Using Base SAS */
/* Create a new variable X containing random numbers between 0 and 1 */
data random;
set EastHigh;
x=ranuni(1234);
run;
/* Sort on the random variable X */
proc sort data=random;
by x;
run;
/* Keep the first n observations. Since the data points are randomly */
/* sorted, these observations constitute a simple random sample. */
data sample2(drop=x);
set random (obs=15);
run;
title "Method 2: DATA step - with sort ";
proc print data=sample2;
run;
/* Method 3: Using SAS DATA Step with no sort required */
data sample3(drop=k n);
/* Initialize K to the number of sample obs needed and N to the */
/* total number of obs in the data set. */
retain k 15 n;
if _n_=1 then n=total;
set EastHigh nobs=total;
/* To randomly select the first observation for the sample, use the */
/* fact that each obs in the data set has an equal chance of being */
/* selected: k/n. If a random number between 0 and 1 is less than */
/* or equal to k/n, we select that the first obs for our sample */
/* and also adjust k and the number of obs needed to complete the */
/* sample. */
if ranuni(1230498) <= k/n then
do;
output;
k=k-1;
end;
/* At every iteration, adjust N, the number of obs left to */
/* sample from. */
n=n-1;
/* Once the desired number of sample points are taken, stop iterating */
if k=0 then stop;
run;
title "Method 3: DATA step, no sort ";
proc print data=sample3;
run;
Method 1: PROC SURVEYSELECT 14:27 Thursday, November 4, 2004 41
Student
Obs GPA Grade ID
1 4.0 9 7
2 2.8 9 11
3 2.4 9 45
4 3.7 9 81
5 3.9 9 100
6 2.8 9 234
7 2.2 9 271
8 4.1 10 19
9 2.8 11 3
10 2.9 12 11
11 3.6 12 59
12 2.1 12 61
13 2.5 12 85
14 2.5 12 100
15 2.6 12 177
Method 2: DATA step - with sort 14:27 Thursday, November 4, 2004 42
Student
Obs GPA Grade ID
1 2.2 11 49
2 2.8 9 27
3 2.7 11 80
4 2.0 12 184
5 2.9 9 101
6 4.0 12 102
7 2.4 9 127
8 2.7 9 93
9 2.8 12 144
10 3.0 12 32
11 2.0 11 5
12 2.7 12 141
13 4.1 12 195
14 2.8 9 234
15 3.8 12 122
Method 3: DATA step, no sort 14:27 Thursday, November 4, 2004 43
Student
Obs GPA Grade ID
1 3.3 9 3
2 3.9 9 10
3 3.5 9 54
4 3.2 9 156
5 3.1 9 161
6 3.0 9 259
7 3.8 9 272
8 3.7 10 3
9 2.4 10 52
10 2.0 11 27
11 2.9 11 77
12 3.4 12 47
13 3.9 12 95
14 3.1 12 126
15 2.7 12 223
Select a random sample where no observation can be
chosen more than once.
| Type: | Sample |
| Topic: | Analytics ==> Survey Sampling and Analysis
SAS Reference ==> Procedures ==> SURVEYSELECT
SAS Reference ==> DATA Step
|
| Date Modified: | 2005-12-08 11:34:26 |
| Date Created: | 2004-09-30 14:09:07 |
Operating System and Release Information
| SAS System | SAS/STAT | All | 8 TS M0 | n/a |
| SAS System | Base SAS | All | 8 TS M0 | n/a |
