(4) Earnings Per Share

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 30, 2017		September 24, 2016		September 30, 2017		September 24, 2016
Average number of common shares outstanding		41,924		42,223		41,957		42,039
Incremental shares from assumed exercises of stock options		89		118		71		131

Average number of common shares and common share equivalents outstanding		42,013		42,341		42,028		42,170

For each of the thirty-nine-week periods ended September 30, 2017 and September 24, 2016, 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.