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):


	Thirty Nine Weeks Ended				Thirteen Weeks Ended
	September 28, 2019		September 29, 2018		September 28, 2019		September 29, 2018
Average number of common shares outstanding		39,891		41,530		39,566		41,101
Incremental shares from assumed exercises of stock options		—		46		—		36

Average number of common shares and common share equivalents outstanding		39,891		41,576		39,566		41,137

For each of the thirty-nine-week periods ended September 28, 2019 and September 29, 2018,

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.