4. Per Share Data

We determine basic earnings per share based on the weighted average number of shares of common stock outstanding during the period and we consider any participating securities for purposes of applying the two-class method. We determine diluted earnings per share based on the weighted average number of shares of common stock outstanding combined with the incremental weighted average shares that would have been outstanding assuming all dilutive potential securities were converted into common shares at the earliest date possible. The following table sets forth the computation of our basic and diluted earnings per share.

	For the Three Months Ended June 30,				For the Six Months Ended June 30,

	*2013*		*2012*		*2013*		*2012*
Net Income attributable to Common Stockholders — Basic and Diluted	$	339,936	$	215,445	$	623,074	$	860,855

Weighted Average Shares Outstanding — Basic		310,261,278		303,252,359		310,124,651		299,472,884
Effect of stock options		—		1,042		103		1,079

Weighted Average Shares Outstanding — Diluted		310,261,278		303,253,401		310,124,754		299,473,963

For the six months ended June 30, 2013, potentially dilutive securities include stock options, units that are exchangeable for common stock and long-term incentive performance, or LTIP, units granted under our long-term incentive performance programs that are convertible into units and exchangeable for common stock. The only securities that had a dilutive effect for the six months ended June 30, 2013 and 2012 were stock options. We accrue dividends when they are declared.