CODEWITHSUNDEEP
rggplot2
Jonathon P
Jonathon P

Reputation: 5

Error Bars appearing too low in ggplot2 bar plot

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.

enter image description here

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.

Upvotes: 0

Views: 557

Answers (1)

Matt
Matt

Reputation: 994

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:

Upvotes: 2

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