Biostatistics

244 CHAPTER 7 HYPOTHESIS TESTING
Dialog box:
Session command:
Stat Basic Statistics 2-Sample t MTB > TwoSample 95.0 C1 C2
SUBC> Alternative 1,
Choose Samples in different columns. Type C1 SUBC> Pooled.
in First and C2 in Second. Click the Options box
and select “less than” in the Alternatives box.
Check Assume equal variances. Click OK.
Output:
Two-Sample T-Test and CI: C, SCI
Two-sample T for C vs SCI
N Mean StDev
C 10 126.1 21.8
SCI 10 133.1 32.2
SE Mean
6.9
10
Difference mu C mu SCI
Estimate for difference: 7.0
95% upper bound for difference: 14.3
T-Test of difference 0 (vs jtj. The default output is a
p value for a two-sided test. The researcher using SAS ® must divide this quantity in half
when the hypothesis test is one-sided. The SAS ® package also tests for equality of
population variances as described in Section 7.8. Figure 7.3.3 shows the SAS ® output
for Example 7.3.2.
Alternatives to z and t Sometimes neither the z statistic nor the t statistic is
an appropriate test statistic for use with the available data. When such is the case, one
may wish to use a nonparametric technique for testing a hypothesis about the difference
between two population measures of central tendency. The Mann-Whitney test statistic
and the median test, discussed in Chapter 13, are frequently used alternatives to the z and
t statistics.