Basic Analysis and Graphing - SAS

158 Performing Oneway Analysis Chapter 5
Equivalence Test
Table 5.19 Description of the Welch’s Test Report
F Ratio
DFNum
DFDen
Prob>F
t Test
Shows the F test statistic for the equal variance test.
See “Statistical Details for the Tests That the Variances Are Equal Report” on
page 181.
Records the degrees of freedom in the numerator of the test. If a factor has k
levels, the numerator has k - 1 degrees of freedom. Levels occurring only
once in the data are not used in calculating the Welch ANOVA. The
numerator degrees of freedom in this situation is the number of levels used
in calculations minus one.
Records the degrees of freedom in the denominator of the test.
See “Statistical Details for the Tests That the Variances Are Equal Report” on
page 181.
Probability of obtaining, by chance alone, an F value larger than the one
calculated if in reality the means are equal across all levels. Observed
significance probabilities of 0.05 or less are considered evidence of unequal
means across the levels.
Shows the relationship between the F ratio and the t Test. Calculated as the
square root of the F ratio. Appears only if the X factor has two levels.
Related Information
• “Example of the Unequal Variances Option” on page 170
• “Statistical Details for the Tests That the Variances Are Equal Report” on page 181
Equivalence Test
Equivalence tests assess whether there is a practical difference in means. You must pick a threshold difference
for which smaller differences are considered practically equivalent. The most straightforward test to
construct uses two one-sided t-tests from both sides of the difference interval. If both tests reject (or
conclude that the difference in the means differs significantly from the threshold), then the groups are
practically equivalent. The Equivalence Test option uses the Two One-Sided Tests (TOST) approach.
Related Information
• “Example of an Equivalence Test” on page 171