[FieldTrip] ANOVA and tails

[Gopakumar Venugopalan]

Well you must have some expectation: Those dependent on alcohol will have a
more diminshed P300 response, than someone who is not. In this case the
postive or negative outcome is a net result of one group having a higher
value (P300) than another group. when you have examining two components P300
and N1 then you have to perform separate tests and/or a multivariate test.
In this case you will also receive some kind or R or correlation statistic
where it show that the two components are inversely related to each other.
That is when P300 increases, then N1 will decrease, and possibly vice versa.

Again I am thinking of all this when the values have been exported to SAS or
SPSS, and not in Fieldtrip.

Warm regards
gopa

On Thu, Sep 1, 2011 at 9:08 AM, Sysoeva, Olga Vladimirovna <
sysoevao at psychiatry.wustl.edu> wrote:

>  Thank you, I understand all of this. I just do not understand why I can
> have more liberal, less conservative criteria (2 tail) in my ANOVA design
> here in Filedtrip.****
>
> I do not have any prior expectation about the result ( for example both
> increase in value for positive component , such as P300, and decrease in
> value for negative component (such as N1) can be considered as increase in
> the amplitude of this components).****
>
> ** **
>
> *From:* fieldtrip-bounces at donders.ru.nl [mailto:
> fieldtrip-bounces at donders.ru.nl] *On Behalf Of *Gopakumar Venugopalan
> *Sent:* Thursday, September 01, 2011 11:58 AM
> *To:* Email discussion list for the FieldTrip project
> *Subject:* Re: [FieldTrip] ANOVA and tails****
>
> ** **
>
> Dear Olga, this does not mean only right tail is possible. You could have a
> positive or negative sign for your test statistic, which is acceptable. That
> can be fixed in Fieldtrip or EEGLAB by the order you enter Condition1 and
> Condition 2. But to answer your question more substantively:****
>
> A one-tail test is more consevervative than a two-tail test. A two-tail
> test is when you have no a priori expectation where you expect the condition
> 1 - condition 2 to be higher or lower. Using a non EEG example if you have
> two groups treatment and control, you will expect yoga to lower the
> depression rates in treatment group and not the control group. ****
>
> Similarly if you have two groups treatment and control, you will expect
> some protein shake to yield higher muscle mass in the treatment group and
> not the control group. In both cases the outcome (negative or lower in
> scenario one, higher or positive on scenario two) is an a priori
> expectation. So in a EEG sense we know that the Incongruent or deviant word
> will have a higher displacement than the congruent or expected word..****
>
> Going back to the conservative versus liberal nature of the statistic.****
>
> If the tabled value of  the F (df1=1, df2=11) is 4.84 that is the size of
> the tail or the reject region, however when you halve that you tabled value
> is half of it. So you obtained value in the first case would have to be
> greater than 4.85, while in the two-tail case it slide with anything over
> 2.43. Therefore the two-tail is not only for exploratory purposes, but is
> also less conservative.****
>
>  ****
>
> I hope I have helped.****
>
>  ****
>
> Warm regards****
>
> gopa****
>
> On Thu, Sep 1, 2011 at 7:51 AM, Sysoeva, Olga Vladimirovna <
> sysoevao at psychiatry.wustl.edu> wrote:****
>
> Dear Fieldtrippers,****
>
> I’ve tried to use between subject ANOVA (independentF) and a bit confused
> with the tails.****
>
> I’ve got the following message****
>
> “For an independent samples F-statistic, it does not make sense to
> calculate a two-sided critical value.”****
>
> Could you explain me why? Why only right tail is possible? ****
>
> Best Regards,****
>
> Olga.****
>
>
> ____________________________________________________________________________
> ****
>
> Olga Sysoeva,****
>
> Research Associate, PhD****
>
> Psychiatry Department,****
>
> Washington University School of Medicine****
>
> Campus Box 8134****
>
> 660 South Euclid Ave****
>
> Saint Louis, MO 63110-9909****
>
>  ****
>
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