Basic earnings (loss) per share is net earnings (loss) divided by the weighted average number of our outstanding common shares, including stock equivalent units where there is no circumstance under which those shares would not be issued. Diluted earnings (loss) per share is net earnings (loss) divided by the sum of the weighted average number of our outstanding common shares and the effect of our outstanding dilutive potential common shares.

	QUARTER ENDED				YEAR-TO-DATE ENDED
SHARES IN THOUSANDS	JUNE 2019		JUNE 2018		JUNE 2019		JUNE 2018
Weighted average common shares outstanding – basic		745,486		757,829		746,041		757,317
Dilutive potential common shares:
Stock options		354		1,628		—		1,655
Restricted stock units		334		512		—		540
Performance share units		58		564		—		480
Total effect of outstanding dilutive potential common shares		746		2,704		—		2,675
Weighted average common shares outstanding – dilutive		746,232		760,533		746,041		759,992

We use the treasury stock method to calculate the dilutive effect of our outstanding stock options, restricted stock units and performance share units. Share-based payment awards that are contingently issuable upon the achievement of specified performance or market conditions are included in our diluted earnings per share calculation in the period in which the conditions are satisfied.

Potential Shares Not Included in the Computation of Diluted Earnings (Loss) per Share

The following shares were not included in the computation of diluted earnings per share because they were either antidilutive or the required performance or market conditions were not met. Some or all of these shares may be dilutive potential common shares in future periods.

	QUARTER ENDED				YEAR-TO-DATE ENDED
SHARES IN THOUSANDS	JUNE 2019		JUNE 2018		JUNE 2019		JUNE 2018
Stock options		2,490		—		2,848		—
Restricted stock units		—		—		359		—
Performance share units		999		486		1,074		486

On February 7, 2019, our board of directors approved and announced a new share repurchase program (the 2019 Repurchase Program) under which we are authorized to repurchase up to $500 million of outstanding shares. Concurrently, the board terminated the remaining repurchase authorization under the share repurchase program approved by the board in November 2015.

During year-to-date 2019, we repurchased over 2.3 million common shares for approximately $60 million under the 2019 Repurchase Program. As of June 30, 2019, we had remaining authorization of approximately $440 million for future share repurchases.

All common share purchases under the share repurchase program are expected to be made in open-market transactions. We record share repurchases upon trade date as opposed to the settlement date when cash is disbursed. We record a liability for repurchases that have not yet been settled as of period end. There were no unsettled repurchases as of June 30, 2019 or December 31, 2018.