(r) Stock-based compensation
Stock-based awards to employees that call for settlement in cash, as deferred share units (“DSUs”) and performance share units (“PSUs”), or that call for settlement in cash at the option of the employee, as stock options awards, are accounted for at fair value and classified as a liability. The compensation cost is recognized in expenses over the vesting period. Changes in the fair value of stock-based awards between the grant date and the measurement date result in a change in the liability and compensation cost.
The fair value of DSUs and PSUs is based on the underlying share price at the date of valuation. The fair value of stock option awards is determined by applying an option pricing model, taking into account the terms and conditions of the grant. Key assumptions are described in note 23.