R.I. Gen. Laws § 44-30-31: Nonresident husband and wife.

(a) If the federal income tax liability of husband or wife, both of whom are nonresidents, is determined on a separate federal return, their Rhode Island tax shall be separately determined.

(b) If the federal income tax liability of husband and wife, both of whom are nonresidents, is determined on a joint federal return, their tax shall be determined on their joint Rhode Island income.

(c) If either husband or wife is a resident and the other is a nonresident, separate taxes shall be determined on their separate Rhode Island incomes on any forms that may be required by the tax administrator, unless both elect to determine their joint Rhode Island income as if both were residents. If separate returns are filed, Rhode Island personal income tax shall be determined as if they had filed separate federal income tax returns.