Let and be the sample standard deviations constructed from
and
, respectively.
When it is reasonable to assume ``
,''
we can construct the *pooled sample variance*

*Confidence interval.*
The following table shows the corresponding confidence interval
of the population mean difference
,
when your null hypothesis is rejected.

Hypothesis testing | -level confidence interval |

vs. . | |

vs. . | |

vs. . |

*Example.*
Suppose that we consider the significant level
,
and that we have obtained
and
from the control group of size ,
and
and
from the experimental group of size .
Here we have assumed that
.
Then we can compute the square root
of the pooled sample variance ,
and the test statistic

Generated by MATH GO: 2006-03-21