What is the percentage change in research and development credits from 2018 to 2019?
{"Amount computed using statutory rate": {"2019": 841, "2018": 2122, "2017": -1078}, "Net change in valuation allowance for net deferred tax assets": {"2019": -459, "2018": -367, "2017": 10058}, "AMT and other": {"2019": "\u2014", "2018": -191, "2017": 20}, "Foreign rate differential": {"2019": 664, "2018": 22, "2017": -169}, "Non-deductible items": {"2019": -151, "2018": -276, "2017": -370}, "State income tax": {"2019": -370, "2018": 50, "2017": -34}, "Impact of tax reform on deferred taxes": {"2019": "\u2014", "2018": -4901, "2017": "\u2014"}, "Research and development credits": {"2019": 1694, "2018": 475, "2017": 2494}, "Foreign income tax": {"2019": -494, "2018": "\u2014", "2017": "\u2014"}, "Stock compensation, net": {"2019": 1539, "2018": "\u2014", "2017": "\u2014"}, "Income tax benefit (provision)": {"2019": 3264, "2018": -3066, "2017": 10921}}
rd_credits_2019 = df["Research and development credits"]["2019"]
rd_credits_2018 = df["Research and development credits"]["2018"]
answer = (rd_credits_2019 - rd_credits_2018) / rd_credits_2018 * 100.0