title: Add significance stars to barplot in ggplot - connected via line
body: <p>I performed a t-test and its p-value suggested the difference between results is significant. I would like to visualize this using stars on <code>ggplot</code>.</p>
  <p>That's how my data looks like:</p>
  <pre><code>&gt; dput(DF_tot)
  structure(list(Names = c(&quot;Mark&quot;, &quot;Nate&quot;, &quot;Stuart&quot;), 
                 Area = c(5.125, 176.115, 7.44), 
                 SD = c(1.87, 3.14, 5.151)), 
            row.names = 4:6, class = &quot;data.frame&quot;)
  </code></pre>
  <p>That's a code I use to create <code>ggplot</code>:</p>
  <pre><code>p &lt;- ggplot(DF_tot, aes(x=Names, y=Area, fill=Names)) + 
    geom_bar(stat=&quot;identity&quot;, fill=&quot;gray12&quot;, position=position_dodge()) +
    geom_errorbar(aes(ymin=Area-SD, ymax=Area+SD), width=.2,
                  position=position_dodge(.9)) 
  
  p + 
    theme_bw() + 
    theme(panel.border = element_blank(), 
          panel.grid.major = element_blank(),
          panel.grid.minor = element_blank(), 
          axis.line = element_line(colour = &quot;black&quot;)) +
    labs(x = &quot;&quot;, y = &quot;&quot;)+
    theme(axis.text=element_text(size=13))
  </code></pre>
  <p>Below I show what I would like to achieve:</p>
  <p><a href="https://i.stack.imgur.com/Ua0ab.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Ua0ab.png" alt="Example" /></a></p>
  <p>Of course such line and stars should also go to the bar on the left side. It would be great if I can easily modify number of stars.</p>