; or (B) to supersede the authority of a State to require combined reporting. 4. Group returns If, in computing the net income tax or other business activity tax liability of a person for a taxable year, the net income or other economic results of affiliated persons is taken into account, the portion of such combined or consolidated net income or other economic results that may be subject to tax by the State shall be computed using the methodology that is generally applicable to businesses conducting similar business activities and, if that generally applicable methodology employs an apportionment formula, the denominator or denominators of that formula shall include the aggregate factors of all persons whose net income or other economic results are included in such combined or consolidated net income or other economic results and the numerator or numerators shall include the factors attributable to the State of only those persons that are themselves subject to taxation by the State pursuant to the provisions of this Act and subject to all other legal constraints on State taxation of interstate or foreign commerce. 5. Definitions and effective date (a) Definitions For purposes of this Act: (1) Net income tax The term net income tax has the meaning given that term for the purposes of the Act entitled An Act relating to the power of the States to impose net income taxes on income derived from interstate commerce, and authorizing studies by congressional committees of matters pertaining thereto , approved September 14, 1959 ( 15 U.S.C. 381 et seq.). (2) Other business activity tax (A) In general The term other business activity tax means any tax in the nature of a net income tax or tax measured by the amount of, or economic results of, business or related activity conducted in the State. (B) Exclusion The term other business activity tax does not include a sales tax, a use tax, or a similar transaction tax, imposed on the sale or acquisition of goods or services, whether or not denominated a tax imposed on the