What is the change in the income tax rates between 2019 and 2018?
{"Statutory federal income tax rate": {"2019": 21.0, "2018": 21.0, "2017": 35.0}, "Effect of:                        -- State income tax, net of federal benefit     ": {"2019": 3.5, "2018": 3.4, "2017": 2.3}, "Effect of:                        -- State credit carryforwards     ": {"2019": 1.3, "2018": 0.3, "2017": -0.1}, "Effect of:                        -- U.S. federal R&D tax credit     ": {"2019": -1.9, "2018": -1.7, "2017": -0.8}, "Effect of:                        -- Tax Reform     ": {"2019": "-", "2018": -0.1, "2017": 1.5}, "Effect of:                        -- Excess benefit of equity compensation     ": {"2019": -0.1, "2018": -0.6, "2017": -1.0}, "Foreign-derived intangible income (FDII)  -- deduction     ": {"2019": -3.1, "2018": -1.6, "2017": "-"}, "Foreign-derived intangible income (FDII)  -- Foreign operations     ": {"2019": 1.1, "2018": 1.2, "2017": -0.1}, "Foreign-derived intangible income (FDII)  -- Tax contingencies     ": {"2019": 3.7, "2018": 0.5, "2017": "-"}, "Foreign-derived intangible income (FDII)  -- Other permanent differences     ": {"2019": 1.5, "2018": 1.0, "2017": 0.3}, "Foreign-derived intangible income (FDII)  -- Change in valuation allowance     ": {"2019": -0.9, "2018": -0.2, "2017": -0.1}, "Foreign-derived intangible income (FDII)  -- Income Tax": {"2019": 26.1, "2018": 23.2, "2017": 37.0}}
income_tax_2019 = df["Foreign-derived intangible income (FDII)  -- Income Tax"]["2019"]
income_tax_2018 = df["Foreign-derived intangible income (FDII)  -- Income Tax"]["2018"]
answer = income_tax_2019 - income_tax_2018