Key points are not available for this paper at this time.
J. Richard Landis, Eugene R. Heyman, Gary G. Koch, Average Partial Association in Three-Way Contingency Tables: A Review and Discussion of Alternative Tests, International Statistical Review / Revue Internationale de Statistique, Vol. 46, No. 3 (Dec., 1978), pp. 237-254
Landis et al. (Fri,) studied this question.