[R] ggplot2, 'se' variable in geom_errorbar's limits?

[Ista Zahn]

Hi Eric,
It's not really a ggplot question. If you are plotting means you can
calculate the standard error as sd/sqrt(n). Then add and subtract the
standard error to create ymax and ymin.

Best,
Ista

On Sat, Feb 19, 2011 at 9:12 PM, Eric Fail <eric.fail at gmx.com> wrote:
> Can't anybody give me a hint on how to solve this? I even bought the
> ggplot2-book, so you could also give a page (or a series of pages).
>
> Thanks,
> Eric
>
> On Thu, Feb 17, 2011 at 10:19 AM, Eric Fail <eric.fail at gmx.com> wrote:
>>
>> Dear R-list
>>
>> I'm working with with geom_errorbar; specifically I'm trying to
>> reproduce the example Hadley Wickham have on
>> http://had.co.nz/ggplot2/geom_errorbar.html (all in the button of the
>> page) where he makes an nice plot with errorbars and then draw lines
>> between the points.
>>
>> What confuses me is the 'limits' he defines for the errorbars from the
>> se variable.
>>
>> First he creates a dataset,
>>
>> df <- data.frame(
>>  trt = factor(c(1, 1, 2, 2)),
>>  resp = c(1, 5, 3, 4),
>>  group = factor(c(1, 2, 1, 2)),
>>  se = c(0.1, 0.3, 0.3, 0.2)
>> )
>>
>> # library(ggplot2)
>>
>> and then he creates some limits from the se variables.
>>
>> limits <- aes(ymax = resp + se, ymin=resp - se)
>>
>> [elements omitted]
>>
>> # and then he creates the plot (I'm interested in).
>>
>> p <- ggplot(df, aes(colour=group, y=resp, x=trt))
>> p + geom_line(aes(group=group)) + geom_errorbar(limits, width=0.2)
>>
>> I can (of course) get Hadley's example to run, but I can't do it on my
>> data as I don't have a 'se' variable/don't know how to create it. I
>> have a group variable, a treatment variable, and a response variable,
>> but no se variable.
>>
>> Could anyone out there explain how I create a 'se' variable in my data?
>>
>> I'm sure my reasoning is the one that is off, and not ggplot2 (I'm a big fan).
>>
>> Your help is appreciated!
>>
>> Thanks,
>> Eric
>
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-- 
Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology
http://yourpsyche.org