A solution to your well taken point would be to impose the tax as a per centage of federal income tax. This would tax cap gains, dividends, and interest. Added benefits would be a simplification in reporting and collection and a built in progressive structure that is inherent in federal taxation. There must be some good reason why other states have adopted this format to collect income tax, and one might assume that this was applied to the long since former, now rescinded, income tax that the state of Alaska used to collect.