test post

[Steve Samuels]

svyset and the other svy commands in Stata apply only to random samples of a defined finite population. Random samples are selected with random numbers. Your n= 40 patients of each types were obviously not selected by random sampling, Therefor no survey sampling analysis is appropriate.

If a simple random sample of size \(n\) is drawn from a population of knwon size \(N\), the probability of selection if \(n/N\) and the sampling weight would be:
\[
wt = \frac{N}{n}
\]
For a brief introduction to random sampling see the introduction to survey commands in the Survey manual.

[Steve Samuels]

Sorry, for the botched mathjax: I did check it in a test post, but added one word. Here's a corrected version of the problem line

The probability of selection is\( n_i/N_i\)and the sampling weight for stratum i would be:

\[
wt_i=\frac{N_i}{n_i}
\]

In your case, \(n_i=40\) would be the denominator and you have to supply the numerator. If the \(N_i\) are unequal, as they will be in practice, than the sampling weights will be unequal.