The
S_TEST
function
tests the
hypothesis that two sample populations *
X*
and *
Y*
have the same mean of distribution against the hypothesis that they differ. The result is a two-element vector containing the maximum number of signed differences between corresponding pairs of *
xi*
and *
yi*
and its one-tailed significance. This type of test is often referred to as the "
Sign Test."

This routine is written in the IDL language. Its source code can be found in the file ```
s_test.pro
```

in the ```
lib
```

subdirectory of the IDL distribution.

Define two *
n*
-element sample populations.

X = [47, 56, 54, 49, 36, 48, 51, 38, 61, 49, 56, 52]

Y = [71, 63, 45, 64, 50, 55, 42, 46, 53, 57, 75, 60]

Test the hypothesis that the two sample populations have the same mean of distribution against the hypothesis that they differ at the 0.05 significance level.

PRINT, S_TEST(X, Y, ZDIFF = zdiff)

The computed probability (0.0729981) is greater than the 0.05 significance level and therefore we do not reject the hypothesis that *
X*
and *
Y*
have the same mean of distribution.