pre_text: Effective Income Tax Rate A reconciliation of the United States federal statutory income tax rate to our effective income tax rate is as follows: In 2019 and 2018 we had pre-tax losses of $19,573 and $25,403, respectively, which are available for carry forward to offset future taxable income. We made determinations to provide full valuation allowances for our net deferred tax assets at the end of 2019 and 2018, including NOL carryforwards generated during the years, based on our evaluation of positive and negative evidence, including our history of operating losses and the uncertainty of generating future taxable income that would enable us to realize our deferred tax.
table: Year Ended Year Ended
table: December 31, 2018 December 31, 2019
table: United States federal statutory rate 21.00% 21.00%
table: State taxes, net of federal benefit 1.99% (0.01)%
table: Valuation allowance (21.96)% (24.33)%
table: Cumulative effect of accounting change — 2.07%
table: R&D Credit 1.34% 1.53%
table: Other (0.38)% (0.27)%
table: Effective income tax rate 1.99% (0.01)%
question: Analyse this data from a financial earnings document. What was the change in the United States federal statutory rate between 2018 and 2019?