15. Earnings Per Share

Basic earnings per share is the amount of earnings (adjusted for dividends declared on preferred stock) available to each share of common stock outstanding during the reporting period. Diluted earnings per share is the amount of earnings available to each share of common stock outstanding during the reporting period adjusted to include the effect of potentially dilutive common shares. Potentially dilutive common shares include incremental shares issued for stock options, restricted stock units and awards, distributions from deferred compensation plans, and the conversion of the Company's convertible preferred stock (See Note 14). Potentially dilutive common shares are excluded from the computation of diluted earnings per share in periods in which the effect would be antidilutive. For diluted earnings per share, net income available to common shares can be affected by the conversion of the Company's convertible preferred stock. Where the effect of this conversion would be dilutive, net income available to common shareholders is adjusted by the associated preferred dividends and deemed dividend. The calculation of basic and diluted earnings per share for each of the three years ended December 31 was as follows:

Approximately 6.6 million, 24.4 million, and 23.6 million options to purchase shares of common stock outstanding at the end of 2013, 2012, and 2011, respectively, were not included in the computation of diluted earnings per share because the effect would be antidilutive.