What is the increase / (decrease) in the ROE(after taxes) from 2018 to 2019?
{"Earnings before taxes (EBT)": {"2019": 632.0, "2018": 633.0}, "ROE (after taxes)": {"2019": 19.1, "2018": 19.7}, "": {"2019": "", "2018": 30.0}, "(in millions of )": {"2019": 2019.0, "2018": 2018.0}, "Total assets": {"2019": 29901.0, "2018": 27628.0}}
roe_2019 = df["ROE (after taxes)"]["2019"]
roe_2018 = df["ROE (after taxes)"]["2018"]
answer = roe_2019 - roe_2018