[FieldTrip] Excluding a subject

[Roni Tibon]

Got it. Awesome :)

Thanks!

On 11 May 2012 10:43, Stephen Whitmarsh <stephen.whitmarsh at gmail.com> wrote:

> Dear Roni & Steve,
>
> Thank you for reminding me one can compare datastructures containing
> means computed by ft_timelockgrandaverage. I forgot about that. Then
> indeed the mean/var has to be re-computed every time if you are trying
> out different subject to reject (and the designmatrix has to stay the
> same). Ofcourse you are rejecting subjects based on a-priori criteria,
> not on the effect it has on the results, so you shouldn't have to do
> it too often ;-)
>
> However, to explain what I meant previously: you do not have to
> compute a grandaverage first, and then do statistics. You can put
> those subjects (of both groups) straight into ft_timelockstatistics,
> and use the designmatrix to specify group membership with 1's and 2's.
> Using a 0 instead for one of your subjects would exclude that subject
> from the analysis.
> (see http://fieldtrip.fcdonders.nl/walkthrough#non-paired_comparison).
>
> Have a nice day!
>
> Stephen
>
>
>
>
> On 10 May 2012 20:55, Roni Tibon <ronitibon at gmail.com> wrote:
> > Dear Stephen and Steve,
> >
> > Thank you for your answers.
> >
> > Stephen, if I understand you correctly, option 1 means I have to compute
> the
> > grand average again (using ft_timelockgrandaverage), which is what I
> tried
> > to avoid.
> >
> > I tried option 2 though, and it didn't work.
> > When I used a zero entry at the uvar line, the data stayed exactly the
> same
> > (as if the subject was not excluded). When I used a zero entry at the
> ivar
> > line (or at both lines), i get an error message saying "invalid
> > specification for the design array".
> >
> > I also tried skipping the entry all together, but got an error message
> > saying "the size of the design matrix does not match the number of
> > observations in the data"
> >
> > An I doing something wrong?
> >
> > Steve, I guess I can do that.. the reason I'm asking is cause I want to
> > "play" with the data a bit - remove a different subjects each time and
> see
> > if I still get the same pattern. So I thought it would be easier if I did
> > not have to compute the grand average again and again.
> >
> > Thanks!
> > Roni
> >
> > On 10 May 2012 14:07, Stephen Whitmarsh <stephen.whitmarsh at gmail.com>
> wrote:
> >>
> >> Hi Tony,
> >>
> >> Thanks for your question.
> >>
> >> First of all, I do not fully understand what you mean with 'without
> >> computing the averages again', but I'll have a shot at it.
> >>
> >> In ft_freq/timelock-statistics you enter all your 'units of
> >> observations', i.e. data structures per subject or condition that you
> >> want to compare, together with the design matrix. The designmatrix is
> >> a one or two row matrix with as many columns as your have
> >> data-entries. One of the rows codes the group/condition membership of
> >> those entries (the independent variable). They can be subjects (group
> >> analysis) or trials (within-subjects analysis). Another row might be
> >> used to code the observation number in case you are doing a paired
> >> test.
> >>
> >> To exclude one data entry (i.e. subject) for your
> >> ft_timelockstatistics you could either:
> >> 1) not enter that datastructure as data in ft_freqstatistics, and also
> >> remove it from your design matrix.
> >> 2) keep your input to ft_timelockstatistics the same but use a zero
> >> for that entry in you design matrix. In this case that data input will
> >> not be used to calculate your statistics.
> >>
> >> I would say the second option is more elegant, but it is more prone to
> >> mistakes perhaps. You would do me a favour if you would doublecheck
> >> that it gives you the same results as option 1.
> >>
> >> I hope this answers your question,
> >>
> >> Stephen
> >>
> >>
> >>
> >> On 10 May 2012 12:09, Roni Tibon <ronitibon at gmail.com> wrote:
> >> > Hi all,
> >> > Is there an elegant way to exclude a subject from the statistical
> >> > analysis
> >> > when using ft_timelockstatistics, without computing the averages again
> >> > while
> >> > excluding the subject?
> >> >
> >> > Thanks!
> >> > Roni
> >> >
> >> > --
> >> >    /\.../\
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> >> >
> >> > http://shkafkafim.blogspot.com/
> >> >
> >> >
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> >
> >
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> >
> >
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