What was the increase / (decrease) in the Custom development income from 2018 to 2019?
{"Licensing of intellectual property including royalty-based fees": {"2019": 367.0, "2018": 723.0, "Yr.-to-Yr. Percent Change": -43.2}, "Custom development income": {"2019": 246.0, "2018": 275.0, "Yr.-to-Yr. Percent Change": -10.5}, "Sales/other transfers of intellectual property": {"2019": 34.0, "2018": 28.0, "Yr.-to-Yr. Percent Change": 22.6}, "Total": {"2019": 648.0, "2018": 1026.0, "Yr.-to-Yr. Percent Change": -36.9}}
custom_development_income_2019 = df["Custom development income"]["2019"]
custom_development_income_2018 = df["Custom development income"]["2018"]
answer = custom_development_income_2019 - custom_development_income_2018