[Eeglablist] statistics in EEGLAB

[Robert Brown]

Dear Arno and All,

thank you very much for your enlightening response.

maybe one idea: let's say that I only have 4 subjects. the statistics based
on "subject means" would be unreliable and I would not get any results.
however, it could be that in case of each single subject there is a
significant difference based on trials in the same time window, which would
actually be a strong evidence for differences between the conditions and
which could be written as "in case of each single subject p < .05
(corrected)". I am sorry if this is not right, but I assume that there could
be instances where the group statistics with 3-4 subjects would not show
anything but the single trial statistics would. (good examples of important
studies with so few subjects would be Tong & Engel, 2001 in Nature with 4
subjects fMRI and Resulaj et al., 2009 in Nature with 3 subjects behavior.).


to conclude: maybe the single trial statistics would work, if it a) would be
calculated individually for each subject based on only this subjects single
trials and then b) the (time-frequency) regions would be plotted, where all
the subjects have significant differences based on their single trial
analysis.

thank you for your attention and good luck,
Bob

2009/11/11 Arnaud Delorme <arno at ucsd.edu>

> Dear Bob,
>
> thanks for the comments. I think you are using the statmode option "trial"
> from the command line. This option is quite experimental. It was implemented
> a while ago and is probably not forward compatible with more recent changes.
> Also, the "statmode", "trials" option (assuming it was working) should only
> be used to plot a single subjects. The reason is based on the type of null
> hypothesis.
>
> When testing with 'statmode', 'subject' for two conditions, the NULL
> hypothesis is: given the subjects I have recorded and given that these
> subjects are a good representation of the general population of all possible
> subjects, there is no difference between the ERP/spectrum/ERSP/ITC between
> the two experimental conditions in the general subject population. Using
> parametric, permutation, or bootstrap statistics (and assumptions) you may
> either accept or reject this hypothesis at a given confidence level.
>
> When testing with 'statmode', 'trial' on a single subject (still two
> conditions), the NULL hypothesis is : given the trials I have recorded and
> given that these trials are a good representation of all the population of
> trials for this subject, there is no difference between the
> ERP/spectrum/ERSP/ITC between the two experimental conditions for this
> subject. Again, using parametric, permutation, or bootstrap statistics (and
> assumptions) you may either accept or reject this hypothesis at a given
> confidence level.
>
> As you can see the two hypothesis are quite different. One makes an
> inference about the population of subjects and the other one about the
> population of trials.
>
> Now if you pool the trials from different subjects and attempt to perform
> statistics, this is going to be more complex. The new hypothesis would then
> be: given the trials I have recorded from my subjects and given that these
> trials are a good representation of all the population of trials from the
> general population of subjects, there is no difference between the
> ERP/spectrum/ERSP/ITC between the two experimental conditions in the general
> population of subjects. But the hypothesis is relatively biased because I
> personally think that all the trials are *not* a good representation of
> all the population of trials from the general population of subjects. The
> trials are a good representation of all the trials from all the subjects
> being presently recorded but not necessarily of the general subject
> population. Therefore the real NULL hypothesis would be : given the trials I
> have recorded from all of my subjects and given that these trials are a good
> representation of all the population of trials from these subjects, there is
> no difference between the ERP/spectrum/ERSP/ITC between the two experimental
> conditions in the recorded subjects. As you see, rejecting the NULL this is
> relatively limited as we care about the general population of subjects and
> not the recorded subjects.
>
> If anybody has some better ideas (or Matlab function) of how to handle the
> subject/trial problem (because it would be nice to include trials in
> statistical analysis in order to make them more powerful), we will take
> them.
>
> Best,
>
> Arno
>
> ps: we will remove the 'statmode', 'trial' option for now.
> pps: for basic inferential statistics, you may also refer to this book
> chapter http://sccn.ucsd.edu/~arno/mypapers/statistics.pdf<http://sccn.ucsd.edu/%7Earno/mypapers/statistics.pdf>
>
> On Nov 11, 2009, at 12:29 AM, Robert Brown wrote:
>
> Dear Arno & others,
>
> this does not seem to be as simple as Arno suggested (but thanks),
>
> 1. I have precomputed the values of these channels (with "savetrials",
> "on")
> 2. these channels all have data
> 3. I can plot the data of the same channels when I use "statmode",
> "subjects"
> 4. I'm using EEGLAB v7.1.3.13b
> 5. I now tried it with v7.1.7.18b and I still get the log of zero error
> (you guys might be interested that in addition I now get, in case of
> permutations and bootstrap, "??? Error using ==> reshape" in
> statcond>surrogate at 438 and statcond at 301 and with this latest version
> the reshape error even happens with the "statmode", "subjects")
>
> thus any other suggestions of what could be happening with my single trial
> analysis in study would be very much appreciated.
>
> thank you very much and take care,
> Bob
>
> 2009/11/11 Arnaud Delorme <arno at ucsd.edu>
>
>> Dear Bob,
>>
>> I think this might be because you are trying to plot ERSP of a channel
>> that contains only 0. This error was also arising in old versions of EEGLAB
>> when masking for significance.
>>
>> Hope this helps,
>>
>> Arno
>>
>>
>> On Nov 7, 2009, at 11:38 AM, Robert Brown wrote:
>>
>>  Hi guys,
>>>
>>> I've been trying to get the study ersp analysis working on single trials
>>> but I've not succeeded.
>>>
>>> in the function "std_readdata" I get the "Warning: Log of zero." error,
>>> which is on the line ersp{c,g} = 20*log10(abs(ersp{c,g})); meaning that the
>>> absolute value at some point is 0.
>>> (This leads to) further errors:
>>>
>>> ??? Error using ==> set
>>> Bad value for axes property: 'CLim'
>>> Values must be increasing and non-NaN.
>>>
>>> Error in ==> caxis at 80
>>>            set(ax,'CLim',arg);
>>>
>>> Error in ==> tftopo at 714
>>> caxis([g.limits(5:6)]);
>>>
>>> I've tried to fix it but I'm not clever enough. any help would be
>>> appreciated.
>>>
>>> thank you so much,,
>>> Bob <ATT00001.txt>
>>>
>>
>>
>
>
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