FAR 15.404-1(b)(2) includes the IGCE as an example among proposal analysis techniques but does not specifically mandate it for price analysis. Likewise, FAR 15.404-1(c)(2)(iii) includes it as an example among cost analysis techniques but again, does not mandate it. Many (if not most) agencies require that purchase request submitters include an estimated unit price so contracting officers have the option to use it as a basis for price analysis. The same points here also apply to modification proposals.