What was the change in the refinance originations between 2017 and 2018?
{"Mortgage loan originations(1): -- Purchase": {"2019": 1272.0, "2018": 1185.0, "2017": 1143.0}, "Mortgage loan originations(1): -- Refinance": {"2019": 796.0, "2018": 458.0, "2017": 616.0}, "Mortgage loan originations(1): -- Total": {"2019": 2068.0, "2018": 1643.0, "2017": 1760.0}}
mortgage_loan_originations1__Refinance_2018 = df["Mortgage loan originations(1): -- Refinance"]["2018"]
mortgage_loan_originations1__Refinance_2017 = df["Mortgage loan originations(1): -- Refinance"]["2017"]
answer = mortgage_loan_originations1__Refinance_2018 - mortgage_loan_originations1__Refinance_2017