Because Connecticut adjusted gross income derived from or connected with sources within this state takes into account only items of income, gain, loss and deduction derived from or connected with Connecticut sources, an apportionment or allocation of items of income, gain, loss and deduction is required when a nonresident individual, or a partnership in which a nonresident individual is a member, carries on a business, trade, profession or occupation partly within and partly without Connecticut.
Conn. Agencies Regs. § 12-711(c)-1