heteroskedasticity

AFNI Message Board
1

Hello,

I conducted a group-level mixed effect ANOVA using 3dMVM in a recent paper and was asked by a reviewer if 3dMVM can account for heteroskedasticity ? I could not find an answer in the documentation.

Thanks for any info !
Pascale

2

Pascale,

Do you have two or more groups? Heteroskedasticity in the sense that those groups may have different variances?

3

Hi Gang,

I have two groups (young and older). Yes, this is how I interpreted this, a potential difference in the variance of the two groups.

Thanks!
Pascale

4

Pascale,

3dMVM does not account for heteroskedasticity because the impact is usually not substantial. Especially when the number of subjects in the two groups is roughly equal, the 3dMVM (as well as the typical two-sample t-test) approach is robust to the presence of unequal variances. However, if this is really a concern, for a test comparing two groups, you can use 3dttest++ -unpooled to perform Welch’s t-test: https://en.wikipedia.org/wiki/Welch’s_t-test