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 September 30,				For the Nine Months Ended September 30,

	*2013*		*2012*		*2013*		*2012*
Net Income attributable to Common Stockholders — Basic and Diluted	$	311,675	$	254,921	$	934,749	$	1,115,776

Weighted Average Shares Outstanding — Basic		310,332,777		304,107,489		310,194,789		301,029,029
Effect of stock options		—		1,070		67		1,077

Weighted Average Shares Outstanding — Diluted		310,332,777		304,108,559		310,194,856		301,030,106

For the nine months ended September 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 nine months ended September 30, 2013 and 2012 were stock options. We accrue dividends when they are declared.