Table:
|  |  | Year Ended December 31, |  |
| --- | --- | --- | --- |
|  | 2019 | 2018 | 2017 |
| Income tax at federal statutory rate | $(10,883) | $(9,811) | $(6,659) |
| Increase (decrease) in tax resulting from: |  |  |  |
| State income tax expense, net of federal tax effect | (3,657) | (2,749) | (421) |
| Nondeductible permanent items | 3,522 | (1,522) | 1,506 |
| Foreign rate differential | (367) | 552 | 599 |
| Tax rate change | — | 134 | 7,226 |
| Adjustment to deferred taxes | (1,904) | 307 | 37 |
| Change in valuation allowance | 22,481 | 15,805 | (2,291) |
| Uncertain tax positions | 128 | 143 | 76 |
| Nonqualified stock option and performance award windfall upon exercise | (9,128) | (1,983) | — |
| Other | 233 | (80) | (26) |
| Total | $425 | $796 | $47 |
Paragraphs:
For purposes of reconciling the Company’s provision for income taxes at the statutory rate and the Company’s provision (benefit) for income taxes at the effective tax rate, a notional 26% tax rate was applied as follows (in thousands):
The difference between the statutory federal income tax rate and the Company’s effective tax rate in 2019, 2018 and 2017 is primarily attributable to the effect of state income taxes, difference between the U.S. and foreign tax rates, deferred tax state rate adjustment, share-based compensation, true up of deferred taxes, other non-deductible permanent items, and change in valuation allowance. In addition, the Company’s foreign subsidiaries are subject to varied applicable statutory income tax rates for the periods presented.
Question:
What was the reason for difference between he statutory federal income tax rate and the Company’s effective tax rate in 2019, 2018 and 2017?
Answer: the effect of state income taxes, difference between the U.S. and foreign tax rates, deferred tax state rate adjustment, share-based compensation, true up of deferred taxes, other non-deductible permanent items, and change in valuation allowance.