What was the increase / (decrease) in the product development Share-based Compensation from 2018 to 2019?
{"Product development": {"2019": 1478, "2018": 1306, "2017": 1545}, "Sales and marketing": {"2019": 469, "2018": 371, "2017": 360}, "General and administrative": {"2019": 2429, "2018": 3011, "2017": 522}, "Total share-based compensation expense": {"2019": 4376, "2018": 4688, "2017": 2427}}
product_development_2019 = df["Product development"]["2019"]
product_development_2018 = df["Product development"]["2018"]
answer = product_development_2019 - product_development_2018