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
SHARES IN THOUSANDS	MARCH 2020		MARCH 2019
Weighted average common shares outstanding – basic		746,534		746,603
Dilutive potential common shares:
Stock options		338		—
Restricted stock units		283		—
Total effect of outstanding dilutive potential common shares		621		—
Weighted average common shares outstanding – dilutive		747,155		746,603

We use the treasury stock method to calculate the dilutive effect of our outstanding stock options, restricted stock units and performance share units.

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 (loss) 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
SHARES IN THOUSANDS	MARCH 2020		MARCH 2019
Stock options		2,292		2,862
Restricted stock units		—		383
Performance share units		1,390		1,356

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 first quarter 2020, we did not repurchase shares. During first quarter 2019, we repurchased over 2.3 million common shares for approximately $60 million under the 2019 Repurchase Program. As of March 31, 2020, we had remaining authorization of approximately $440 million for future share repurchases. All common stock repurchases under the 2019 Repurchase Program were made in open-market transactions.