AFNI Message Board

Dear AFNI users-

We are very pleased to announce that the new AFNI Message Board framework is up! Please join us at:

https://discuss.afni.nimh.nih.gov

Existing user accounts have been migrated, so returning users can login by requesting a password reset. New users can create accounts, as well, through a standard account creation process. Please note that these setup emails might initially go to spam folders (esp. for NIH users!), so please check those locations in the beginning.

The current Message Board discussion threads have been migrated to the new framework. The current Message Board will remain visible, but read-only, for a little while.

Sincerely, AFNI HQ

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B. Douglas Ward
November 22, 2002 05:02PM

Hello Liz:

The F-test for factor C (subject) random effect requires repetitions of the
experiment. This means that there must be more than one sample per cell
(i.e., n > 1).

A "cell" refers to a particular combination of factor levels (A, B, and C).
From Table 4 of the 3dANOVA3 documentation, we see that calculation of F(C)
requires estimation of MSE. However, from Table 2, we see that estimation
of MSE requires n > 1. Hence, if there is only one sample per cell (n = 1),
then it is not possible to test for factor C effect.

To put this in English: In order to determine if there is a subject effect,
it is necessary to compare the subject-to-subject variation (MSC) with the pure
measurement error (MSE). But MSE can be estimated only if we have repetitions
of the entire experiment.

Usually, the factor C (subject) random effect is not of inherent interest.

Doug Ward
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Subject Author Posted

error message in 3dANOVA3

Liz Roy November 20, 2002 01:51PM

Re: error message in 3dANOVA3

B. Douglas Ward November 22, 2002 05:02PM