“…Other portfolio models have been developed since then, focusing on clients (e.g., Turnbull & Zolkiewski, 1997), on suppliers (e.g., Olsen & Ellram, 1997;Bensaou, 1999;Nellore & Söderquist, 2000;Hartmann, Ritter, & Gemünden, 2001;Gelderman & van Weele, 2002) or generally on business relationships (Krapfel, Salmond, & Spekman, 1991;Zolkiewski & Turnbull, 2000). These matrix models vary in terms of the factors, factor weights, or number of analysis steps.…”