We compute basic earnings per common share by dividing net income attributable to Core Laboratories N.V. by the weighted average number of common shares outstanding during the period. Diluted earnings per share includes the incremental effect of contingently issuable shares from performance and restricted stock awards, as determined using the treasury stock method. The following table summarizes the calculation of weighted average common shares outstanding used in the computation of basic and diluted earnings per share (in thousands):


	Three Months Ended
	March 31,
	2023		2022
Weighted average common shares outstanding - basic		46,634		46,298
Effect of dilutive securities:
Restricted shares		105		—
Performance shares		742		—
Weighted average common shares outstanding - diluted		47,481		46,298

For the three months ended March 31, 2022, the number of outstanding performance and restricted shares of Core Laboratories N.V. common shares that were excluded from the diluted earnings per share calculation, as their impact would be antidilutive, were as follows (in thousands):

Three Months Ended

March 31, 2022

Restricted shares

Performance shares