title: How to superimpose bar plots in R?
body: <p>I'm trying to create a figure similar to the one below (taken from Ro, Russell, &amp; Lavie, 2001). In their graph, they are plotting bars for the errors (i.e., accuracy) within the reaction time bars.  Basically, what I am looking for is a way to plot bars within bars. </p>
  
  <p><img src="https://i.stack.imgur.com/cmrZT.jpg" alt="stacked bar chart"></p>
  
  <p>I know there are several challenges with creating a graph like this. First, Hadley points out that it is not possible to create a graph with two scales in ggplot2 because those graphs are fundamentally flawed (see <a href="https://stackoverflow.com/questions/3099219/plot-with-2-y-axes-one-y-axis-on-the-left-and-another-y-axis-on-the-right">Plot with 2 y axes, one y axis on the left, and another y axis on the right</a>)</p>
  
  <p>Nonetheless, the graph with superimposed bars seems to solve this dual sclaing problem, and I'm trying to figure out a way to create it in R. Any help would be appreciated.</p>