# [R] Means do not tally

Ruijie breakaway8 at gmail.com
Mon May 24 17:10:56 CEST 2010

```Noted.

I have attached a list of some data in csv format.

The first column is the SubID and the rest of the column are the mean of
each condition for the particular subject.

Average 1 is the average computed from each column in the list.
Average 2 is computed from the raw data of all the data points of a
condition.

The difference is typically at the 3rd decimal place. If anyone needs the
raw data, I could supply it after some clean up.

I suspected round of errors but in all procedures in R, I retained 14
significant figures. How would the round off error affect the 3rd decimal
place?

Any ideas anyone?

Regards,
Ruijie (RJ)

--------
He who has a why can endure any how.

~ Friedrich Nietzsche

On 24 May 2010 22:47, jim holtman <jholtman at gmail.com> wrote:

> It is hard to tell what you are doing without data and the results you
> have gotten so far:
>
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
>
> On Mon, May 24, 2010 at 10:35 AM, Ruijie <breakaway8 at gmail.com> wrote:
> > Hi all,
> >
> > here is my situation
> >
> > In my experiment, I expose 10 subjects to 24 different conditions of
> > stimuli. Each condition is exposed to the same subject 3x.
> > This would make each subject have 24x3=72 data points. All the subjects
> > combined would have 72x10=720 data points with each condition having 30
> > datapoints.
> >
> > To find the grand average of each condition, I find the average of all
> the
> > datapoints for a given condition.
> >
> > To find the SD for each condition, if I use the raw dataset (720
> datapoints)
> > it would not reflect the SD across subjects. Therefore, I compute the
> > average for each condition per subject .i.e. For subject 1, I would find
> the
> > average of condition 1 (average across 3 trials). and so on.
> > With the average of each condition per subject, I then compute the SD.
> >
> > Since I computed the average of each condition per subject,
> theoretically,
> > if i average the average of each condition per subject across all
> subjects,
> > the result would be the same as the grand average.
> >
> > However, this is not the case when I use R or Excel. regardless of
> functions
> > used. Anyone have any thoughts?
> >
> > Regards,
> > Ruijie (RJ)
> >
> > --------
> > He who has a why can endure any how.
> >
> > ~ Friedrich Nietzsche
> >
> >        [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help at r-project.org mailing list
> > 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.
> >
>
>
>
> --
> Jim Holtman
> Cincinnati, OH
> +1 513 646 9390
>
> What is the problem that you are trying to solve?
>
```