Item 6. Selected Financial Data Consolidated Statements of Income Data for the years ended December 31, 2010, 2009, and 2008 and  Consolidated Balance Sheet Data as of December 31, 2010 and 2009  from our audited Consolidated Financial Statements included in  this Annual Report on Form 10-K. The Consolidated Statements of  Income Data and Other Consolidated Financial Data for the years  ended December 31, 2007 and 2006 and Consolidated Balance Sheet  Data as of December 31, 2008, 2007, and 2006 were derived from  our audited Consolidated Financial Statements, as restated, that  are not included in this Annual Report on Form 10-K. The selected historical financial data shown below should be read  in conjunction with Management’s Discussion and Analysis of  Financial Condition and Results of Operations and our Consolidated  Financial Statements and related notes included elsewhere in this  Annual Report on Form 10-K. We have derived our Consolidated  Statements of Income Data and Other Consolidated Financial Data (in thousands except per share amounts)  2006  2007  2008  2009  2010 Revenue  $ 315,175  $ 435,107  $ 502,457  $ 478,996  $ 555,351 Operating expense (1)   237,648   318,086  363,581   354,323  434,292 Operating income (1)  77,527  117,021   138,876   124,673  121,059 Non-operating income, net  4,164  6,229  4,252  2,934  6,732 Income before income taxes, equity in net income 81,691   123,250  143,128   127,607  127,791 of unconsolidated entities, and cumulative effect of accounting change (1) Income tax expense (1)  34,094  51,610  54,423  46,775  42,756 Equity in net income of unconsolidated entities  2,787  1,694  1,321  1,165  1,422 Consolidated income before cumulative effect of 50,384  73,334  90,026  81,997  86,457 accounting change (1) Cumulative effect of accounting change, 259  —  —  —  — net of tax of $171 (3)  Consolidated net income (1)  50,643  73,334  90,026  81,997  86,457 Net (income) loss attributable to noncontrolling interests  —  —  (397)  132  (87) Net income attributable to Morningstar, Inc. (1)  $ 50,643  $ 73,334  $ 89,629  $ 82,129  $ 86,370 Net income per share attributable to Morningstar, Inc.: Basic (1)  $  1.23  $  1.70  $  1.94  $  1.71  $  1.75 Diluted (1)  $  1.08  $  1.52  $  1.82  $  1.65  $  1.70 Weighted average common shares outstanding:  Basic  41,176  43,216  46,139  48,112  49,249 Diluted  46,723  48,165  49,213  49,793  50,555 Morningstar, Inc. 2010 Annual Report 57