We investigated bias, sampling variability, Type I error and power of nine approaches for testing the group by time interaction in a repeated measures design under three types of missing data mechanisms. One procedure due to Overall, Ahn, Shivakumar, and Kalburgi (1999) performed reasonably well over a range of conditions.
Algina, James; Keselman, H. J.; and Othman, Abdul R.
"Analyzing Group by Time Effects in Longitudinal Two-Group Randomized Trial Designs With Missing Data,"
Journal of Modern Applied Statistical Methods: Vol. 2
, Article 6.
Available at: http://digitalcommons.wayne.edu/jmasm/vol2/iss1/6