What was the percentage change in the amount of research and development between 2018 and 2019?
{"Stock-based compensation expense data: -- Sales and marketing": {"2019": 2075, "2018": 1196, "2017": 561}, "Stock-based compensation expense data: -- General and administrative": {"2019": 6474, "2018": 4901, "2017": 2638}, "Stock-based compensation expense data: -- Research and development": {"2019": 12054, "2018": 7332, "2017": 4214}, "Stock-based compensation expense data: -- Total stock-based compensation expense": {"2019": 20603, "2018": 13429, "2017": 7413}}
research_and_development_2019 = df["Stock-based compensation expense data: -- Research and development"]["2019"]
research_and_development_2018 = df["Stock-based compensation expense data: -- Research and development"]["2018"]
answer = ( research_and_development_2019 - research_and_development_2018 ) / research_and_development_2018 * 100.0