Key points are not available for this paper at this time.
John W. Finney, Roger E. Mitchell, Ruth C. Cronkite, Rudolph H. Moos, Methodological Issues in Estimating Main and Interactive Effects: Examples from Coping/Social Support and Stress Field, Journal of Health and Social Behavior, Vol. 25, No. 1 (Mar., 1984), pp. 85-98
Finney et al. (Thu,) studied this question.