What is the change in the Research and development credits from 2018 to 2019?
{"Federal statutory rate": {"2019": 21.0, "2018": 24.5, "2017": 35.0}, "Foreign rate differential": {"2019": 1.6, "2018": 5.1, "2017": 31.9}, "State taxes net of federal benefit": {"2019": 0.9, "2018": 0.8, "2017": 0.2}, "Warrant liabilities": {"2019": "\u2014", "2018": 4.4, "2017": -1.8}, "Change in valuation allowance": {"2019": -2.4, "2018": 34.0, "2017": -270.0}, "Research and development credits": {"2019": 1.4, "2018": 9.0, "2017": 12.8}, "Provision to return adjustments": {"2019": 0.3, "2018": 8.3, "2017": -4.0}, "Section 382 adjustment": {"2019": -19.3, "2018": "\u2014", "2017": "\u2014"}, "Nondeductible compensation expense": {"2019": -0.6, "2018": 1.4, "2017": -4.1}, "Global Intangible Low Taxed Income": {"2019": -2.9, "2018": "\u2014", "2017": "\u2014"}, "Nondeductible legal fees": {"2019": "\u2014", "2018": 0.9, "2017": -3.9}, "2017 tax reform": {"2019": "\u2014", "2018": -73.7, "2017": "\u2014"}, "Intra-entity license transfer": {"2019": 9.4, "2018": "\u2014", "2017": "\u2014"}, "Other permanent differences": {"2019": -0.1, "2018": -0.9, "2017": 0.1}, "Effective income tax rate": {"2019": 9.3, "2018": 13.8, "2017": -203.8}}
research_and_development_credits_2019 = df["Research and development credits"]["2019"]
research_and_development_credits_2018 = df["Research and development credits"]["2018"]
answer = research_and_development_credits_2019 - research_and_development_credits_2018