# Two Groups (One Factor/Two Levels), One Covariates

This models the input as two lines. If DODS, then each line has its own intercept and slope. If DOSS, then each line has its own intercept but they share a slope.

### FSGD File

```GroupDescriptorFile 1
Title OSGM
Class Group1
Class Group2
Variable Age
Input subject1 Group1 30
Input subject2 Group2 40```

Nclasses = 2
Nvariables = 1

### Regressors

Nregressors = Nclasses*(Nvariables+1) = 2*(1+1) = 4
Regressor1: ones for subjects in Group 1, 0 otherwise. Codes intercept/mean for Group 1
Regressor2: ones for subjects in Group 2, 0 otherwise. Codes intercept/mean for Group 2
Regressor3: age for subjects in Group 1, 0 otherwise. Codes age slope for Group 1
Regressor4: age for subjects in Group 2, 0 otherwise. Codes age slope for Group 2

### Contrasts

##### Contrast1

Null Hypothesis: is there a difference between the group intercepts?

Contrast File: g1-g2.intercept.mtx

`1 -1 0 0`

Since this is a t-test, the output will be signed, with Group1>Group2 being positive (red/yellow). Reversing the sign will only change the sign of the output, not its magnitude.

##### Contrast2:

Null Hypothesis: is there a difference between the group slopes? Note: this is an interaction between group and age. Note: not possible to test with DOSS

Contrast File: g1-g2.slope.mtx

`0 0 1 -1`

Since this is a t-test, the output will be signed, with Group1>Group2 being positive (red/yellow). Reversing the sign will only change the sign of the output, not its magnitude.

===== Contrast3: ===== Null Hypothesis: does Group1 differ from Group2 in intercept or slope?

Contrast File: g1-vs-g2.mtx

```1 -1 0  0
0  0 1 -1 ```

Note: this is an F-test (and hence unsigned).

##### Contrast4

Null Hypothesis: does mean of group intercepts differ from 0?

Contrast File: g1g2.intercept.mtx

`0.5 0.5 0 0`

##### Contrast5

Null Hypothesis: does mean of group slopes differ from 0?

Contrast File: g1g2.intercept.mtx

`0 0 0.5 0.5`