Thanks. I appreciate this isn't strictly an R question and will
pursue on another list.
The procedure I followed was inspired from
@article{
Author = {Baayen, R. Harald and Milin, Petar},
Title = {Analysing Reaction Times},
Journal = {International Journal of Psychological Research},
Volume = {3},
Number = {2},
Pages = {12--28},
Year = {2010} }
Best,
Cecile
On 18 April 2012 19:55, Bert Gunter <gunter.ber...@gene.com> wrote:
>
> Cecile:
>
> On Wed, Apr 18, 2012 at 8:21 AM, Cecile De Cat <c.de...@leeds.ac.uk> wrote:
> > Hello,
> >
> > I'm analysing reaction time data from a linguistic experiment (a variant of
> > a lexical decision task). To ascertain that the data was normally
> > distributed, I used *shapiro.test *for each participant (see commands
> > below), but only one out of 21 returns a p value above p.0 05.
> >
> >> f = function(dfr) return(shapiro.test(dfr$Target.RTinv)$p.value)
> >> p = as.vector(by(newdat, newdat$Subject, f))
> >> names(p) = levels(newdat$Subject)
> >> names(p[p < 0.05])
> >
> > Removing a few outliers
>
> !! Yikes!! I won't say "Don't do this." But I will say that this can
> be a very dangerous and unscientific thing to do, leading to biased,
> misleading results.
>
> per subject doesn't make a difference, and
> > "aggressive" removal of outliers (done by subject, for each of the 6
> > conditions ) still results in non-normally distributed data by subject.
> >
> > Does this invalidate any attempt at multi-level modelling?
>
> How can we possibly know without knowing in detail the objectives of
> the investigation, the nature of the data, and the details of the
> analysis you did??!
>
> On general principles, normality is rarely of any real importance;
> lack of independence (or, in general, non-adherence to the covariance
> structures specified) usually is. So "any attempt" seems too general
> a claim to support. Indeed, a good graphical analysis -- often the
> most scientifically informative thing to do anyway -- is almost always
> a good thing to do.
>
> As this has little to do with R, you should follow up on a statistical
> list, like stats.stackexchange.com .
>
> -- Bert
> >
> > Many thanks in advance for your help.
> >
> > Cecile
> >
> > [[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.
>
>
>
> --
>
> Bert Gunter
> Genentech Nonclinical Biostatistics
>
> Internal Contact Info:
> Phone: 467-7374
> Website:
> http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm
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