What is the change in the expected volatility in 2019?
{"Weighted average fair value per option granted": {"2019": 2.34, "2018": 2.13}, "Weighted average share price": {"2019": 58.0, "2018": 57.0}, "Weighted average exercise price": {"2019": 58.0, "2018": 56.0}, "Expected dividend growth": {"2019": 5.0, "2018": 5.0}, "Expected volatility": {"2019": 14.0, "2018": 12.0}, "Risk-free interest rate": {"2019": 2.0, "2018": 2.0}, "Expected life (years)": {"2019": 4.0, "2018": 4.0}}
expected_volatility_2019 = df["Expected volatility"]["2019"]
expected_volatility_2018 = df["Expected volatility"]["2018"]
answer = expected_volatility_2019 - expected_volatility_2018