30. Alternative Method Figure 7-6 and Table 7-1 summarize the decisions made when choosing between the normal and t distributions. An alternative method included in some textbooks (but almost never included in professional journals) is based on this criterion: Substitute the sample standard deviation s for whenever n . 30, then proceed as if is known. Assume that for a simple random sample, n 5 35, and s 5 10.0, then construct 95% confidence interval estimates of using the method of this section and using the alternative method. Compare the results.