Hi David, thanks for the quick response. I did look at the help files for
model.tables and se.contrast and neither seemed appropriate. I probably
wasn't clear enough in my original email, so here's more information:
I'm analyzing data from a psychology experiment on how people allocate
visual attention when walking over difficult terrain. In the experiment
subjects walked on a treadmill for 30 minutes while performing an
attention-demanding reaction time task. In one condition they could walk
freely, whereas in another condition they had to avoid markings placed on
the treadmill belt to simulate obstacles. The stimuli for the reaction time
task were placed either at eye-level or near the ground.
The dependent measure I'm working with comes from an eye-tracking system
that we ran while subjects walked, which provided data on the amount of time
subjects looked at the reaction time stimuli versus the treadmill belt. We
divided the fixation time data sets for each subject into three time bins to
look at changes in fixation behavior over time.
So the full design of the study is a 2x2x2x3 with repeated measures on all
factors. The factors were:
Markings (Levels: present, absent)
Reaction time task "Position" (Levels: eye-level, ground-level)
Eye fixation "Plane": (Levels: RT stimuli, treadmill belt)
Time bin (Levels: 1,2,3)
A call to aov yields main effects of Markings, Position, and Plane, as well
as a Markings*Plane interaction. For comparison purposes I ran the same
analysis in SPSS and got equivalent ANOVA results, so I'm confident the
model has been set up properly in R.
Now, what I want to get are means and standard errors for the main effects
and interaction to generate figures for publication using other software. As
stated in my initial post, I got the means using model.tables and they are
correct as compared with the SPSS output. However, I cannot get the standard
errors for the means. I've tried various things in R and cannot get values
that correspond to the SPSS output.
Again, I assume there is an R function that can get me the values I need and
would hugely appreciate any pointers. In case you're wondering why I'm
bothering with running the analyses in R given that I already have them done
in SPSS, I'm just generally interested in learning to use R to have an
additional analysis tool in my toolkit.
Thanks for any help!
Cheers,
Jason
On Sat, Dec 13, 2008 at 9:04 AM, David Winsemius wrote:
>
> On Dec 12, 2008, at 10:59 PM, JS.Augustyn@gmail.com wrote:
>
> Hi all,
>>
>> I'm quite new to R and have a very basic question regarding how one gets
>> the standard error of the mean for factor levels under aov. I was able to
>> get the factor level means using:
>>
>> summary(print(model.tables(rawfixtimedata.aov,"means"),digits=3)),
>>
>> where rawfixtimedata.aov is my aov model. It doesn't appear that there is
>> an equivalent function to get the standard errors for the factor levels.
>>
>> I searched through the help archives and documentation but could not find
>> anything that would help resolve my problem. I'm sure there is a trivial
>> solution, but I would sincerely appreciate having someone more expert
>> dispel my ignorance.
>>
>>
> Have you looked at the help page for model.tables? ... and perhaps
> ?se.contrast
>
> There are arguments to that function that result in standard errors for
> _effects_. If standard errors on the contrasts are not what you wanted, then
> perhaps a full example would help.
>
> --
> David Winsemius
>
>
> Cheers,
>>
>> Jason Augustyn
>>
>> [[alternative HTML version deleted]]
>>
>> ______________________________________________
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>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
>
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