In the case of a joint return of spouses in a marriage, pursuant to ORS § 316.122 or pursuant to ORS § 316.367, the tax imposed by ORS § 316.037 shall be twice the tax which would be imposed if the taxable income were cut in half. For purposes of this section, a return of a head of household or a surviving spouse, as defined in subsections (a) and (b) of section 2 of the Internal Revenue Code, shall be treated as a joint return of spouses in a marriage. [1969 c.493 § 12; 1975 c.674 § 2; 1987 c.293 § 7; 1987 c.647 § 10; 2015 c.629 § 40]