What was the percentage change in Stock-based compensation expense between 2018 and 2019?
{"Net sales (1)": {"2019": 1382818.0, "2018": 1200181.0, "2017": 757338.0}, "Cost of sales (1)": {"2019": 924276.0, "2018": 860744.0, "2017": 571944.0}, "Gross Margin (GAAP) (1)": {"2019": 458542.0, "2018": 339437.0, "2017": 185394.0}, "Gross margin as a % of net sales": {"2019": 33.2, "2018": 28.3, "2017": 24.5}, "Non-GAAP adjustments: -- Plant start-up costs (2)": {"2019": -927.0, "2018": 929.0, "2017": 427.0}, "Non-GAAP adjustments: -- Stock-based compensation expense": {"2019": 2756.0, "2018": 1519.0, "2017": 1384.0}, "Non-GAAP adjustments: -- Adjusted gross margin (non-GAAP) (1)": {"2019": 460371.0, "2018": 341885.0, "2017": 187205.0}, "Non-GAAP adjustments: -- Adjusted gross margin as a % of net sales": {"2019": 33.3, "2018": 28.5, "2017": 24.7}}
stock_compensation_2019 = df["Non-GAAP adjustments: -- Stock-based compensation expense"]["2019"]
stock_compensation_2018 = df["Non-GAAP adjustments: -- Stock-based compensation expense"]["2018"]
answer = (stock_compensation_2019 - stock_compensation_2018) / stock_compensation_2018 * 100.0