The two-sided 100(1 − α
) confidence interval for the difference of means has the following expression:
For more information on how to calculate the fitted means and the standard error of the difference, go to Methods and formulas for fitted means in Fit Mixed Effects Model.
Calculations for the test statistic, adjusted p-value, individual confidence level, and grouping information table match the calculations for general linear models. For more information, go to the Methods and Formulas for comparisons for general linear models.
The critical value is from the Studentized Range Distribution with tail probability α
levels of the fixed effect term or the random term, and df degrees of freedom:
|the quantile from the studentized range distribution with df degrees of freedom|
| the simultaneous probability of making a Type I error|
|m||the number of levels in the term|
|df||the degrees of freedom|
The degrees of freedom depend on whether the comparison is for a fixed effect term or a random term.
Degrees of freedom (df)
For a fixed effect term, the degrees of freedom (df) are the same as the degrees of freedom for testing the corresponding fixed effect term. For a random term, the degrees of freedom use Satterthwaites approximation method.
For more information on the calculation of the degrees of freedom, go to Methods and formulas for tests of fixed effects in Fit Mixed Effects Model.