title: How to add shaded confidence intervals to line plot with specified values
body: <p>I have a small table of summary data with the odds ratio, upper and lower confidence limits for four categories, with six levels within each category.  I'd like to produce a chart using ggplot2 that looks similar to the usual one created when you specify a lm and it's se, but I'd like R just to use the pre-specified values I have in my table.  I've managed to create the line graph with error bars, but these overlap and make it unclear.  The data look like this:</p>
  
  <pre><code>interval    OR  Drug    lower   upper
  14  0.004   a   0.002   0.205
  30  0.022   a   0.001   0.101
  60  0.13    a   0.061   0.23
  90  0.22    a   0.14    0.34
  180 0.25    a   0.17    0.35
  365 0.31    a   0.23    0.41
  14  0.84    b   0.59    1.19
  30  0.85    b   0.66    1.084
  60  0.94    b   0.75    1.17
  90  0.83    b   0.68    1.01
  180 1.28    b   1.09    1.51
  365 1.58    b   1.38    1.82
  14  1.9 c   0.9 4.27
  30  2.91    c   1.47    6.29
  60  2.57    c   1.52    4.55
  90  2.05    c   1.31    3.27
  180 2.422   c   1.596   3.769
  365 2.83    c   1.93    4.26
  14  0.29    d   0.04    1.18
  30  0.09    d   0.01    0.29
  60  0.39    d   0.17    0.82
  90  0.39    d   0.2 0.7
  180 0.37    d   0.22    0.59
  365 0.34    d   0.21    0.53
  </code></pre>
  
  <p>I have tried this:</p>
  
  <pre><code>limits &lt;- aes(ymax=upper, ymin=lower)
  dodge &lt;- position_dodge(width=0.9)
  ggplot(data, aes(y=OR, x=days, colour=Drug)) + 
    geom_line(stat="identity") + 
    geom_errorbar(limits, position=dodge)
  </code></pre>
  
  <p>and searched for a suitable answer to create a pretty plot, but I'm flummoxed!</p>
  
  <p>Any help greatly appreciated!</p>