The Mixed-Up Suite The Mixed-up Suite provides mixed-effects
regression functionality not available anywhere else—at
any price. MIXOR, MIXREG, MIXNO and MIXPREG are based on the
collaborative effort of
Drs. Donald Hedeker and Robert D. Gibbons of the University
of Illinois at Chicago. Discerning Systems Inc. produced the
user interfaces around the computer programs written by Don
Hedeker. The work was supported by the National Institute of
Mental Health and the MacArthur Foundation, and the programs
are available free of charge for download from the MIXOR/MIXREG
homepage located at the University of Illinois at Chicago.
BIFACTOR
The BIFACTOR program estimates the bifactor model for ordinal and dichotomous
data.
RMASS
The RMASS program computes sample size for three-level mixed-effects linear regression
models for the analysis of clustered longitudinal data. Three-level designs
are used in many areas, but in particular, multi-center randomized longitudinal
clinical trials in medical or health-related research. In this case, level
1 represents measurement occasion, level 2 represents subject, and level 3
represents center. The model allows for random-effects of the time trends at
both the subject-level and the center-level. The sample size determinations
in this program are based on the requirements for a test of treatment by time
interaction(s) for designs based on either subject-level or cluster-level randomization.
The approach is general with respect to sampling proportions and number of
groups, and it allows for differential attrition rates over time.
The general methodology is discussed in Sample
Size Determination for Hierarchical Longitudinal Designs with Differential
Attrition Rates
