Table:
| (In millions of dollars, except tax rates) | Years ended December 31 |  |  |
| --- | --- | --- | --- |
|  | 2019 | 2018 | %Chg |
| Adjusted EBITDA 1 | 6,212 | 5,983 | 4 |
| Deduct (add): |  |  |  |
| Depreciation and amortization | 2,488 | 2,211 | 13 |
| Gain on disposition of property, plant and equipment | - | (16) | (100) |
| Restructuring, acquisition and other | 139 | 210 | (34) |
| Finance costs | 840 | 793 | 6 |
| Other income | (10) | (32) | (69) |
| Income tax expense | 712 | 758 | (6) |
| Net income | 2,043 | 2,059 | (1) |
Paragraphs:
INCOME TAX EXPENSE
Below is a summary of the difference between income tax expense computed by applying the statutory income tax rate to income before income tax expense and the actual income tax expense for the year.
Our effective income tax rate this year was 25.8% compared to 26.9% for 2018. The effective income tax rate for 2019 was lower than the statutory tax rate primarily as a result of a reduction to the Alberta corporate income tax rate over a four-year period.
Question:
What caused the decrease in effective tax rate from 2018 to 2019?
Answer: reduction to the Alberta corporate income tax rate over a four-year period