title: Plot the observed and fitted values from a linear regression using xyplot() from the lattice package
body: <p>I can create simple graphs. I would like to have observed and predicted values (from a linear regression) on the same graph. I am plotting say <code>Yvariable</code> vs <code>Xvariable</code>. There is only 1 predictor and only 1 response. How could I also add linear regression curve to the same graph?</p>
  
  <p>So to conclude need help with:</p>
  
  <ul>
  <li>plotting actuals and predicted both</li>
  <li>plotting regression line</li>
  </ul>