In exercises that call for two-sample procedures, you may use either of the two approximations for the degrees of freedom that we have discussed: the value given by your software or the smaller of and . Be sure to state clearly which approximation you have used.
7.72 Pooled equals unpooled?
The software outputs in Figure 7.10 (pages 387–388) give the same value for the pooled and unpooled statistics. Do some simple algebra to show that this is always true when the two sample sizes and are the same. In other cases, the two statistics usually differ.