title: Interpretation of "stat_summary = mean_cl_boot" at ggplot2?
body: <p>a perhaps simple question
  I tried to make an errorgraph like the one shown in page 532 of Field's "Discovering Statistics Using R".</p>
  
  <p>The code can be found here <a href="http://www.sagepub.com/dsur/study/DSUR%20R%20Script%20Files/Chapter%2012%20DSUR%20GLM3.R">http://www.sagepub.com/dsur/study/DSUR%20R%20Script%20Files/Chapter%2012%20DSUR%20GLM3.R</a> :</p>
  
  <pre><code>line &lt;- ggplot(gogglesData, aes(alcohol, attractiveness, colour = gender))
  line + stat_summary(fun.y = mean, geom = "point") + 
  stat_summary(fun.y = mean, geom = "line", aes(group= gender)) + 
  stat_summary(fun.data = mean_cl_boot, geom = "errorbar", width = 0.2) + 
  labs(x = "Alcohol Consumption", y = "Mean Attractiveness of Date (%)", colour = "Gender")  
  </code></pre>
  
  <p>I produced the same graph; my y-axis variable has only 4-points (it is a discrete scale, 1-4), now the y-axis has the points 1.5, 2, 2.5 in which the lines vary.</p>
  
  <p>And the question is: what do these points and graphs describe?
  I assume that the important part is <code>stat_summary(fun.data = mean_cl_boot, geom = "errorbar", width = 0.2)</code> are they count of observations for that group and that level(x-axis)? Are they frequencies? Or, are they proportions? </p>
  
  <p>I found this <a href="http://docs.ggplot2.org/0.9.3/stat_summary.html">http://docs.ggplot2.org/0.9.3/stat_summary.html</a> but it did not help me</p>
  
  <p>Thank you</p>