What is the increase / (decrease) in the Adjusted EBITDA margin from 2018 to 2019?
{"Orders": {"2019": 16244.0, "2018": 15198.0, "Actual": 7.0, "Comp.": 4.0}, "Revenue": {"2019": 15225.0, "2018": 14445.0, "Actual": 5.0, "Comp.": 3.0}, "therein: product business": {"2019": 5530.0, "2018": 5302.0, "Actual": 4.0, "Comp.": 2.0}, "Adjusted EBITA": {"2019": 1500.0, "2018": 1574.0, "Actual": -5, "Comp.": ""}, "Adjusted EBITA margin": {"2019": 9.9, "2018": 10.9, "Actual": "", "Comp.": ""}}
adjusted_ebita_margin_2019 = df["Adjusted EBITA margin"]["2019"]
adjusted_ebita_margin_2018 = df["Adjusted EBITA margin"]["2018"]
answer = adjusted_ebita_margin_2019 - adjusted_ebita_margin_2018