Dunnett’s Pairwise Multiple Comparison

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This test compares each group with the first group. Prior to selecting this test you need to specify these comparisons and remove any NET from the columns of the table.

The test statistic is:

t=\frac{\bar x_1-\bar x_2}{\sqrt{\frac{\sum^{J}_{j=1}\sum^{n_j}_{i=1} w_{ij}(x_{ij} - \bar x_j)^2}{v}(\frac{1}{e_1}+\frac{1}{e_1})}}

where:

\bar x_1 and \bar x_2 are the means of the two groups being compared and \bar x_j is the mean of the j of J groups,
when applying the test to Repeated Measures, each respondent’s average is initially subtracted from their data and it is this corrected data that constitutes of x_{ij},
n_j is the number of observations in the jth of J groups,
w_{ij} is the Calibrated Weight for the ith observation in the j group,
e_j is the Effective Sample Size for the j group,
v = (J - 1)(\sum^J_{j=1} e_j - 1) for Repeated Measures and v = \sum^J_{j=1} e_j - J - 1 otherwise.
t is evaluated using a multivariate t distribution (see Dunnett C. W. (1955.) "A multiple comparison procedure for comparing several treatments with a control", Journal of the American Statistical Association, 50:1096–1121).

Circumstances when this test is applied

See also