14. Employee future benefits (continued):

Components of net benefit expense recognized are as follows:

	2019	2018
Current service cost	$ 1,949	$ 2,528
Interest cost	2,541	2,297
Net benefit expense	$ 4,490	$ 4,825

Net benefit expense for the year is recognized as administrative expense on the consolidated statement of income.

The main actuarial assumptions underlying the valuation are as follows:

(a) Health care cost trend rates:

The health care cost trend for prescription drugs is estimated to increase at 6.5% in 2020 grading down to 4.0% by 2041. Other health expenses are estimated to increase at 5.0% grading down to 4.0% by 2041. Dental expenses are estimated to increase at 4.0% per year.

(b) Financial instruments:

The liabilities at the period end and the present value of future liabilities were determined using a discount rate of 3.1% (2018 – 4.0%) representing an estimate of the yield on high quality corporate bonds as at the valuation date.

(c) Mortality decrement:

The rates applicable to public sector retirees in the 2014 Canadian Pensioners Mortality table produced by the Canadian Institute of Actuaries were used as the basis of these assumptions.

A 1% or one year change in actuarial assumptions, assuming all other factors remain constant, has the following impact on the defined benefit liability carrying amount:

	December 31, 2019		December 31, 2018
	Increase	Decrease	Increase	Decrease
Health care trend rate (1% change)	$ 10,335	$ (8,260)	$ 12,236	$ (9,605)
Discount rate (1% change)	$ (9,534)	$ 12,782	$(10,312)	$ 13,390
Mortality (1 year)	$ 2,540	$ (2,460)	$ 2,817	$ (2,721)