pre_text: 15. AVERAGE SHARES OUTSTANDING Our basic earnings per share calculation is computed based on the weighted-average number of common shares outstanding. Our diluted earnings per share calculation is computed based on the weighted-average number of common shares outstanding adjusted by the number of additional shares that would have been outstanding had the potentially dilutive common shares been issued. Potentially dilutive common shares include nonvested stock awards and units, stock options, and non-management director stock equivalents. Performance share awards are included in the average diluted shares outstanding each period if the performance criteria have been met at the end of the respective periods. The following table reconciles basic weighted-average shares outstanding to diluted weighted-average shares outstanding in each fiscal year (in thousands):
table: 2019 2018 2017
table: Weighted-average shares outstanding — basic 25,823 28,499 30,630
table: Effect of potentially dilutive securities:
table: Nonvested stock awards and units 211 240 182
table: Stock options 10 40 59
table: Performance share awards 24 28 43
table: Weighted-average shares outstanding — diluted 26,068 28,807 30,914
table: Excluded from diluted weighted-average shares outstanding:
table: Antidilutive 186 150 76
table: Performance conditions not satisfied at the end of the period 65 44 53
question: Analyse this data from a financial earnings document. What is the difference in nonvested stock awards and units between 2018 and 2019?