5. PER SHARE DATA 6. INVESTMENT PROPERTIES Investment properties consist of the following as of December 31: 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 common shares were converted into  shares at the earliest date possible. The following table sets forth the computation of our basic and diluted earnings per share. For the year ending December 31, 2011, 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 year ended  December 31, 2011 and 2010 were stock options. The only securities that had a dilutive effect for the year ended December 31,  2009 were stock options and contingently issuable shares from stock dividends. We accrue dividends when they are declared. The taxable nature of the dividends declared for each of the years ended as  indicated is summarized as follows: 2011 2010 Land $ 3,136,981 $ 2,929,054 Buildings and improvements   26,196,349 24,263,169 Total land, buildings and improvements   29,333,330 27,192,223 Furniture, fixtures and equipment  323,716 316,512 Investment properties at cost   29,657,046 27,508,735 Less — accumulated depreciation  8,388,130 7,711,304 Investment properties at cost, net  $21,268,916 $ 19,797,431 Construction in progress included above  $ 464,076 $  125,227 For the Year Ended December 31, 2011 2010 2009 Total dividends paid per common share  $3.50  $2.60  $2.70 Percent taxable as ordinary income  98.30% 53.82% 99.3% Percent taxable as long-term capital gains  1.70% 39.68% 0.7% Percent nontaxable as return of capital  — 6.50% — 100.0% 100.0% 100.0% For the Year Ended December 31, 2011 2010 2009 Net Income attributable to Common Stockholders — Basic $ 1,021,462 $  610,424 $  283,098 Effect of dilutive securities: Impact to General Partner’s interest in Operating Partnership from all dilutive securities and options  39 97 50 Net Income attributable to Common Stockholders — Diluted $ 1,021,501 $  610,521 $  283,148 Weighted Average Shares Outstanding — Basic  293,504,064 291,076,008 267,054,946 Effect of stock options  69,408 2 74,460 315,897 Effect of contingently issuable shares from stock dividends  — — 1,101,307 Weighted Average Shares Outstanding — Diluted 293,573,472   291,350,468 268,472,150 2011 Annual Report 49