title: comparing two linear models in R
body: <p>Let's say I have two linear models in R such that:</p>
  
  <p><strong>lm1 = (x ~ a + b)</strong></p>
  
  <p><strong>lm2 = (x ~ a + b + c)</strong></p>
  
  <p>I want to determine <strong>the effect of c on x</strong> in terms of </p>
  
  <p>1) significance of effect
  2) estimate of effect
  3) c's contribution towards overall variation in x (e.g. c's component of the R-squared value)</p>
  
  <p><strong>anova(lm1, lm2)</strong> provides me with a significance figure but not the other figures I need, particularly 3 above.</p>
  
  <p>How do I go about computing these figures?</p>