Earnings per common share attributable to Landstar System, Inc. and subsidiary are based on the weighted average number of shares outstanding, including outstanding

non-vested

restricted stock and outstanding Deferred Stock Units. Diluted earnings per share attributable to Landstar System, Inc. and subsidiary are based on the weighted average number of common shares and Deferred Stock Units outstanding plus the incremental shares that would have been outstanding upon the assumed exercise of all dilutive stock options.

The following table provides a reconciliation of the average number of common shares outstanding used to calculate earnings per common share attributable to Landstar System, Inc. and subsidiary to the average number of common shares and common share equivalents outstanding used to calculate diluted earnings per share attributable to Landstar System, Inc. and subsidiary (in thousands):


	Thirteen Weeks Ended
	March 28, 2020		March 30, 2019
Average number of common shares outstanding		39,254		40,161
Incremental shares from assumed exercises of stock options		—		5

Average number of common shares and common share equivalents outstanding		39,254		40,166

For each of the thirteen-week periods ended March 28, 2020 and March 30, 2019, no options outstanding to purchase shares of common stock were antidilutive. Outstanding RSUs were excluded from the calculation of diluted earnings per share attributable to Landstar System, Inc. and subsidiary for all periods because the performance metric requirements or market condition for vesting had not been satisfied.