What was the change in Research expenditures between 2018 and 2019?
{"Post-retirement benefits": {"2019": 1100, "2018": 1061}, "Inventory reserves": {"2019": 708, "2018": 1236}, "Loss carry-forwards": {"2019": 4724, "2018": 4647}, "Credit carry-forwards": {"2019": 15964, "2018": 16909}, "Accrued expenses": {"2019": 4932, "2018": 5685}, "Research expenditures": {"2019": 17953, "2018": 16847}, "Operating lease liabilities": {"2019": 6211, "2018": "\u2014"}, "Stock compensation": {"2019": 2232, "2018": 2142}, "Foreign exchange loss": {"2019": 1986, "2018": 2245}, "Other": {"2019": 230, "2018": 207}, "Gross deferred tax assets": {"2019": 56040, "2018": 50979}, "Depreciation and amortization": {"2019": 12453, "2018": 11500}, "Pensions": {"2019": 13552, "2018": 11736}, "Operating lease assets": {"2019": 5963, "2018": "\u2014"}, "Subsidiaries' unremitted earnings": {"2019": 1903, "2018": 1258}, "Gross deferred tax liabilities": {"2019": 33871, "2018": 24494}, "Net deferred tax assets": {"2019": 22169, "2018": 26485}, "Deferred tax asset valuation allowance": {"2019": -8011, "2018": -8274}, "Total net deferred tax assets": {"2019": 14158, "2018": 18211}}
research_expenditures_2019 = df["Research expenditures"]["2019"]
research_expenditures_2018 = df["Research expenditures"]["2018"]
answer = research_expenditures_2019 - research_expenditures_2018