a regression analysis was performed and the summary output is shown below. regression statistics multiple r 0.723834007 r square 0.523935670 adjusted r square 0.503237221 standard error 8.654929901 observations 145 anova df ss ms f significance f regression 6 11,376.758 1896.126 25.3128 4.0187e-20 residual 138 10,337.278 74.908 total 144 21,714.036 step 1 of 2 : how many independent variables are included in the regression model?