40
Stata Technical Bulletin
STB-58
in the resulting 12 (2x2x3) different strata are given in the following table.
|
sex |
weight |
alive |
deceased |
|
male |
<60 |
160^^ |
8- |
|
60-70 |
1,083 |
33 | |
|
>70 |
5,418 |
103 | |
|
female |
<60 |
440 |
18- |
|
60-70 |
407 |
26 |
>70 378 14
We decided to sample 10 pilot observations from each stratum. One stratum had only 8 observations available, so all of
these were included in the pilot sample. The resulting pilot data are available in the dataset wtpilot.dta, which can be loaded
as follows and the coding command run to see in which order we should enter the vector of prevalences for the strata.
. use wtpilot
. coding mort sex wtcat
|
grp.yz |
mort |
sex |
Wtcat |
grp_z |
nobs |
|
1 |
0 |
0 |
1 |
1 |
10 |
|
2 |
0 |
0 |
2 |
2 |
10 |
|
3 |
0 |
0 |
3 |
3 |
10 |
|
4 |
0 |
1 |
1 |
4 |
10 |
|
5 |
0 |
1 |
2 |
5 |
10 |
|
6 |
0 |
1 |
3 |
6 |
10 |
|
7 |
1 |
0 |
1 |
1 |
8 |
|
8 |
1 |
0 |
2 |
2 |
10 |
|
9 |
1 |
0 |
3 |
3 |
10 |
|
10 |
1 |
1 |
1 |
4 |
10 |
|
11 |
1 |
1 |
2 |
5 |
10 |
|
12 |
1 |
1 |
3 |
6 |
10 |
for functions requiring first stage sample sizes∕prevalences
enter these in the order of grp_yz
This tells us that our prevalence vector should be
. matrix prev=(0.02,.134,.670,.054,.05,.047,.001,.004,.013,.002,.003,.002)'
and we can find the design which will optimize (i.e., minimize) the variance of Ivedb subject to a total budget of £10,000.
. optbud mort sex-surg,first(sex wtcat)
prev(prev) var(7) b(10000) cl(2) c2(15)
the second stage sample sizes
----------+.
group(mor I
t sex I
wtcat) I
----------+.
1
2
3
4
5
6
7
8
9
10
11
12
----+.
Freq.
10
10
10
10
10
10
8
10
10
10
10
10
|
please check the sample sizes ! | ||||||
|
grp.yz |
mort |
sex |
Wtcat |
grp_z |
prev |
n2-pilot |
|
1 |
0 |
0 |
1 |
1 |
.02 |
10 |
|
2 |
0 |
0 |
2 |
2 |
.134 |
10 |
|
3 |
0 |
0 |
3 |
3 |
.67 |
10 |
|
4 |
0 |
1 |
1 |
4 |
.054 |
10 |
|
5 |
0 |
1 |
2 |
5 |
.05 |
10 |
|
6 |
0 |
1 |
3 |
6 |
.047 |
10 |