Error Bars appearing too low in ggplot2 bar plot

Question

Been scouring the site (and others) for a solution to the problem pictured below. I can't get the error bars to move from their 'low' position, despite trying lots of different solutions to similar problems I have encountered here and elsewhere.

The problem occurs whether I produce one graph alone or the two and combine them with gridExtra.

Here is the code and a sample of each dataset included:

First dataset example:

Group      PSQI Time_Point
1 Control    2   Baseline
2 Control    2   Baseline
3 Control    2   Baseline
4 Control   13   Baseline
5 Control    1   Baseline
6 Control    7   Baseline

Second:

  Group    ESS Time_Point
1 Control   3   Baseline
2 Control   4   Baseline
3 Control   1   Baseline
4 Control   0   Baseline
5 Control   7   Baseline
6 Control  11   Baseline

Code:

library(gridExtra)
library(ggplot2)
library(grid)

p1 <- ggplot(PSQI_Graph,aes(fill=Group,y=PSQI,x=Time_Point)) +
    geom_bar(position="dodge",stat="identity", width = 0.50) +
    stat_summary(fun.data = mean_cl_normal, geom = "errorbar", position = 
position_dodge(.5), width = .25)+
    guides(fill = F)+
    scale_y_continuous(name = "Mean PSQI Score", limits=c(0,25))+
    xlab("Time Point") +
    guides(fill = guide_legend(keywidth = 1.5, keyheight = 1))+
    theme_bw()

Would really like to get this data out, so would appreciate any suggestions.

Welcome to SO. Please edit your question and provide a reproducible example that showcases your problem and that is ready to copy-paste-run in a new R session. — lukeA
– lukeA, Commented Jun 9, 2017 at 12:28
If you calculate mean for both levels in each facet, you'll notice that the center of the error bars is right where mean is. — Roman Luštrik
– Roman Luštrik, Commented Jun 9, 2017 at 12:57

Matt · Accepted Answer · 2017-06-09 12:53:19Z

2

It would be better to use geom_errorbar. First, you'll have to make a new data.frame with one line per bar, including the standard error (I added an "After" timepoint to show how this looks):

    Group PSQI Time_Point StdErr
1 Control 4.50   Baseline   1.91
2 Control 7.17      After   0.79

Then, this ggplot call will work:

ggplot(psqi, aes(fill=Group, y=PSQI, x=Time_Point, ymin=PSQI-StdErr, ymax=PSQI+StdErr)) + #the ymin and ymax parameters here tell it where to put the top and bottom error bars
    geom_bar(stat="identity") +
    geom_errorbar() #you can change the width and thickness of the bars

Yielding this image:

answered Jun 9, 2017 at 12:53

Matt

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1 Comment

Jonathon P Over a year ago

Worked perfectly! Legend!

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