title: Comparing nonlinear regression models
body: <p>I want to compare the curve fits of three models by r-squared values. I ran models using the <code>nls</code> and <code>drc</code> packages. It appears, though, that neither of those packages calculate r-squared values; they give "residual std error" and "residual sum of squares" though. </p>
  
  <p>Can these two be used to compare model fits?</p>