Computes i_a = i + f + i*f.
References
Tziner, A., Meir, E. I., Dahan, M., & Birati, A. (1994). An investigation of the predictive validity and economic utility of the assessment center for the high- management level. Canadian Journal of Behavioural Science, 26, 228-245.
Holling, H. (1998). Utility analysis of personnel selection: An overview and empirical study based on objective performance measures. Methods of Psychological Research Online, 3(1), 5-24.