The group attribute defines a set of subject numbers for which the variable assignments apply.
integer | A positive integer indicating which subject numbers belong to the group. |
modulus | A positive integer indicating the modulus. |
variablename | The name of a variable to be substituted in the script with its associated value. |
value | The name of an element in the script to substitute for the variablename. |
The group attribute defines a group of subjects based on subject number who share the same condition of a between subjects variable. A given subject is in the group if the following is true:
integer = remainder( subjectnumber / modulus )
If a given subject number falls within the group, the variable is replaced with the element name specified by value whereever it occurs in the script. Multiple groups can be defined to create different experimental conditions. A single subject number can only be assigned to one group.
The following specifies that for odd numbered subjects, the first block is "conditiona" and for even numbered subjects, the first block is "conditionb".
<variables>
/group=(1 of 2) (block1=conditiona)
/group=(2 of 2) (block1=conditionb)
</variables>
The following specifies that the first two of every four subjects (e.g., 1, 2, 5, 6, 9, 10, ...) are presented "redprime" and "redtarget". The third and fourth of every four subjects are shown "blueprime" and "bluetarget".
<variables>
/group=(1, 2 of 4) (prime=redprime, target=redtarget)
/group=(3, 4 of 4) (prime=blueprime, target=bluetarget)
</variables>
The following specifies that every three subjects run "condition1", "condition2", and "condition3" respectively for the first trial.
<variables>
/group=(1 of 3) (trial1=condition1)
/group=(2 of 3) (trial2=condition2)
/group=(3 of 3) (trial3=condition3)
</variables>