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Earnings and Dividends per Share | 12 Months Ended
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Dec. 31, 2020
Earnings and Dividends Per Share [Abstract] |
Earnings per Share | Earnings and Dividends per Share The Company has unvested restricted stock units outstanding that are considered participating securities and, therefore, computes basic and diluted earnings per share under the two-class method. Basic earnings per share for the periods are based upon the weighted average number of shares of common stock outstanding during the periods. Diluted earnings per share include the effects of certain stock options and performance stock units.
|  | Year Ended December 31,
|  | 2020 |  | 2019 |  | 2018
Net income attributable to Westlake Chemical Corporation |  | $ | 330 |  |  | $ | 421 |  |  | $ | 996 |
Less: |  |  |  |  |  |
Net income attributable to participating securities |  | (1) |  |  | (2) |  |  | (5) |
Net income attributable to common shareholders |  | $ | 329 |  |  | $ | 419 |  |  | $ | 991 |
The following table reconciles the denominator for the basic and diluted earnings per share computations shown in the consolidated statements of operations:
|  | Year Ended December 31,
|  | 2020 |  | 2019 |  | 2018
Weighted average common shares—basic |  | 127,850,592 |  |  | 128,395,184 |  |  | 129,401,823 |
Plus incremental shares from: |  |  |  |  |  |
Assumed exercise of options and vesting of performance stock units |  | 238,466 |  |  | 362,109 |  |  | 583,930 |
Weighted average common shares—diluted |  | 128,089,058 |  |  | 128,757,293 |  |  | 129,985,753 |
Earnings per common share attributable to Westlake Chemical Corporation: |  |  |  |  |  |
Basic |  | $ | 2.57 |  |  | $ | 3.26 |  |  | $ | 7.66 |
Diluted |  | $ | 2.56 |  |  | $ | 3.25 |  |  | $ | 7.62 |
Excluded from the computation of diluted earnings per share for the years ended December 31, 2020, 2019 and 2018 are options to purchase 1,151,776, 562,773 and 150,479 shares of common stock, respectively. These options were outstanding during the periods reported but were excluded because the effect of including them would have been antidilutive. Dividends per Share Dividends per common share for the years ended December 31, 2020, 2019 and 2018 were as follows:
|  | Year Ended December 31,
|  | 2020 |  | 2019 |  | 2018
Dividends per common share |  | $ | 1.0650 |  |  | $ | 1.0250 |  |  | $ | 0.9200 |

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