[[FsgdExamples|Back to FSGD Examples]]

~+'''One Group (One Factor), Two Covariates'''+~

This models the input with a single offset for the group with two
slopes, one for each covariate/continuous factor (eg, Age and
Weight). DODS and DOSS will give the same results.

<<TableOfContents>>

= FSGD File (g1v2.fsgd) =
{{{
GroupDescriptorFile 1
Title G1V2
Class Main
Variables Age Weight
Input subject1 Main 30 100
Input subject2 Main 40 120
}}}

Nclasses = 1 <<BR>>
Nvariables = 2 <<BR>>

= Regressors (DODS) =

Nregressors = Nclasses*(Nvariables+1) = 1*(2+1) = 3 (DODS and DOSS) <<BR>>
Regressor1: All ones. Codes intercept/mean for Main<<BR>>
Regressor2: age for each subject. Codes age slope for Main<<BR>>
Regressor3: weight for each subject. Codes age slope for Main<<BR>>

= Contrasts =
The number of columns in each contrast matrix must be the same as the
number of regressors (Nregressors). If there is only one row in the
contrast matrix, then the result will be a t-test and will have a
sign. Reversing the signs in the contrast matrix will only change the
sign of the output, not its magnitude. If there is more than one row,
the result will be an F-test and will be unsigned. 

== Contrast 1 main.mtx ==
Null Hypothesis: the intercept/offset is different than 0 after
regressing out the effects of age and weight.

{{{
1 0 0
}}}

This is a t-test with offset>0 being positive (red/yellow).

== Contrast 2 age.mtx ==

{{{
0 1 0
}}}

This is a t-test with the age slope>0 being positive (red/yellow). 

== Contrast 3 weight.mtx ==

{{{
0 0 1
}}}

This is a t-test with the weight slope>0 being positive (red/yellow). 

== mri_glmfit command ==

This is an example invocation of mri_glmfit. Depending upon your
application, you may have other options as well.

{{{
mri_glmfit \
  --glmdir g1v2 \
  --y y.mgh \
  --fsgd g1v2.fsgd \
  --C main.mtx \
  --C age.mtx \
  --C weight.mtx 
}}}