[FieldTrip] Statistics: comparing conditions with different sample size

[Yoni Levy]

Hi Julian

I indeed meant comparing within subject conditions, one with many more
trials than the other (e.g. 500 vs 100 trials). I am aware that this
difference would bias my result, the question is whether there might be a
way to bypass such bias, without the conservative solution of equating the
trial number in both conditions (i.e. removing 400 trials from condition1,
and thereby comparing 100 vs 100).
One possible solution that was suggested was to proceed with an indepT
test, and then proceeding with an "spm_t2z" transformation ; yet, I wonder
whether this is also valid for such large difference between sample sizes.

Thanks
Yoni


On Thu, Jan 22, 2015 at 1:00 PM, <fieldtrip-request at science.ru.nl> wrote:

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>    1. Statistics: comparing conditions with different sample    size
>       (Yoni Levy)
>    2. Re: Statistics: comparing conditions with different       sample
>       size (Julian Keil)
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> Message: 1
> Date: Thu, 22 Jan 2015 08:54:07 +0200
> From: Yoni Levy <yoniilevy at gmail.com>
> To: fieldtrip at science.ru.nl
> Subject: [FieldTrip] Statistics: comparing conditions with different
>         sample  size
> Message-ID:
>         <CAFEs3xRzvnNgM=2=
> QiybRRQvQ-QfTRpWgj0it4oPLr8BnkSHLA at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
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> Is there a way in FT to deal with the statistical comparison of conditions
> with different sample size (for instance N = 500 vs N = 100)?
>
> Thanks for any input
> Yoni
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> Message: 2
> Date: Thu, 22 Jan 2015 09:05:20 +0100
> From: Julian Keil <julian.keil at gmail.com>
> To: FieldTrip discussion list <fieldtrip at science.ru.nl>
> Subject: Re: [FieldTrip] Statistics: comparing conditions with
>         different       sample size
> Message-ID: <FEA47AF1-F080-4B4B-9FFD-EB7F8B4E5C11 at gmail.com>
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> Dear Yoni,
>
> do you mean different *group* sizes (as in 500 patients vs. 100 controls)?
> Then use the stat fun indepsamplesT.
> If you mean 500 trials vs 100 trials within one subject, you can again use
> the indepsamplesT-function, but beware! The number of trials can severely
> influence your signal.
> I personally strongly suggest using the same number of trials and subjects.
>
> Best,
>
> Julian
>
>
> ********************
> Dr. Julian Keil
>
> AG Multisensorische Integration
> Psychiatrische Universit?tsklinik
> der Charit? im St. Hedwig-Krankenhaus
> Gro?e Hamburger Stra?e 5-11, Raum E 307
> 10115 Berlin
>
> Telefon: +49-30-2311-1879
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>
> http://psy-ccm.charite.de/forschung/bildgebung/ag_multisensorische_integration
>
> Am 22.01.2015 um 07:54 schrieb Yoni Levy:
>
> > Is there a way in FT to deal with the statistical comparison of
> conditions with different sample size (for instance N = 500 vs N = 100)?
> >
> > Thanks for any input
> > Yoni
> > _______________________________________________
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