  We describe a modified sequential probability ratio test that can be used to
reduce the average sample size required to perform statistical hypothesis tests
at specified levels of significance and power. Examples are provided for $z$
tests, $t$ tests, and tests of binomial success probabilities. A description of
a software package to implement the test designs is provided. We compare the
sample sizes required in fixed design tests conducted at 5$\%$ significance
levels to the average sample sizes required in sequential tests conducted at
0.5$\%$ significance levels, and we find that the two sample sizes are
approximately equal.
