What is the increase / (decrease) in revenue from 2018 to 2019?
{"Selected Statement of Income Data -- Revenue": {"2019": 270126.0, "2018": 261253.0, "2017": 252994.0, "2016": 274428.0, "2015": 284175.0}, "Selected Statement of Income Data -- Cost of sales": {"2019": -155396.0, "2018": -134708.0, "2017": -164240.0, "2016": -172764.0, "2015": -155777.0}, "Selected Statement of Income Data -- Gross profit": {"2019": 114730.0, "2018": 126545.0, "2017": 88754.0, "2016": 101664.0, "2015": 128398.0}, "Selected Statement of Income Data -- Administrative costs": {"2019": -87134.0, "2018": -68029.0, "2017": -63309.0, "2016": -64019.0, "2015": -49546.0}, "Selected Statement of Income Data -- Operating profit before exceptional item": {"2019": 27596.0, "2018": 58516.0, "2017": 25445.0, "2016": 37645.0, "2015": 78852.0}, "Selected Statement of Income Data -- Impairment loss": {"2019": -423335.0, "2018": "\u2014", "2017": "\u2014", "2016": "\u2014", "2015": "\u2014"}, "Selected Statement of Income Data -- Operating profit/(loss)": {"2019": -395739.0, "2018": 58516.0, "2017": 25445.0, "2016": 37645.0, "2015": 78852.0}, "Selected Statement of Income Data -- Net finance costs": {"2019": -7674.0, "2018": -17813.0, "2017": -17156.0, "2016": -8010.0, "2015": -5861.0}, "Selected Statement of Income Data -- Other gains/(losses), net": {"2019": 288.0, "2018": -41321.0, "2017": 14205.0, "2016": -3636.0, "2015": -10483.0}, "Selected Statement of Income Data -- Profit/(loss) before tax": {"2019": -403125.0, "2018": -618.0, "2017": 22494.0, "2016": 25999.0, "2015": 62508.0}, "Selected Statement of Income Data -- Income tax": {"2019": -7328.0, "2018": -9127.0, "2017": -11039.0, "2016": -12711.0, "2015": -13178.0}, "Selected Statement of Income Data -- Profit/(loss) for the year (1)": {"2019": -410453.0, "2018": -9745.0, "2017": 11455.0, "2016": 13288.0, "2015": 49330.0}, "(Loss)/Earnings per share (cents) -- Basic (loss)/earnings per share": {"2019": -599.5, "2018": -36.3, "2017": 6.4, "2016": 6.6, "2015": 74.3}, "(Loss)/Earnings per share (cents) -- Diluted (loss)/earnings per share": {"2019": -599.5, "2018": -36.3, "2017": 5.1, "2016": 5.2, "2015": 72.4}, "Weighted average number of ordinary shares -- Basic": {"2019": 70707.0, "2018": 62151.0, "2017": 59410.0, "2016": 57732.0, "2015": 54278.0}, "Weighted average number of ordinary shares -- Diluted": {"2019": 72170.0, "2018": 63482.0, "2017": 60943.0, "2016": 59036.0, "2015": 54969.0}, "Other non-GAAP measures -- Gross Revenue (2)": {"2019": 304593.0, "2018": 268069.0, "2017": 252994.0, "2016": 274428.0, "2015": 284175.0}, "Other non-GAAP measures -- EBITDA (3)": {"2019": -393188.0, "2018": 20186.0, "2017": 42548.0, "2016": 36294.0, "2015": 70066.0}, "Other non-GAAP measures -- Adjusted EBITDA (3)": {"2019": 103845.0, "2018": 82955.0, "2017": 55664.0, "2016": 70852.0, "2015": 101150.0}, "Other non-GAAP measures -- Gross Adjusted EBITDA (3)": {"2019": 234000.0, "2018": 198240.0, "2017": 190980.0, "2016": 199155.0, "2015": 218404.0}}
revenue_2019 = df["Selected Statement of Income Data -- Revenue"]["2019"]
revenue_2018 = df["Selected Statement of Income Data -- Revenue"]["2018"]
answer = revenue_2019 - revenue_2018