## Reference
Participant Groups

The participant groups feature in SuperLab lets you perform two main things:

- Specify which blocks are presented and the order that they are presented in. This gives you a way of specifying counterbalancing sequences.

- Control when trials within a block, events within a trial, or trial variable levels are randomized.

Participant groups can be used when you need to divide your population of participants into groups based on certain factors such as age or gender; or to test a dependent variable.

Because of the way SuperLab works, at least one group is always required. Due to this, SuperLab automatically creates a new group when you create a new experiment. You can edit this group and rename it. But you cannot delete the last group in an experiment.

### Editing Groups

In this example, we will create two participant groups, one for left handed participants and another for right handed ones. We will assume that four blocks have already been created: “Instructions”, “All Participants”, “Left Handed Participants”, and “Right Handed Participants”.

In SuperLab:

- Click on the Experiment menu and select Participant Groups. A dialog appears showing the list of existing groups. If you haven’t created or edited groups yet, the dialog will show only one group named “Main Group”.

- Click on the Edit button to edit “Main Group”. The Group Editor appears.

- In the Group Name edit field, change “Main Group” to “Left Handed Group”.

- In the Blocks to Run tab, click on the Run only the following blocks radio button. The list below it becomes enabled and all four existing blocks have their blue checkboxes turned on.

- Click on the “Right Handed Participants” checkbox to turn it off.

- Notice how the Group Editor has an up arrow and a down arrow. These can be used to re-arrange the order in which blocks are presented.

- Click on the OK button to close the Group Editor dialog.

Now let’s create the second group:

- Click on the New button. The Group Editor appears

- In the Group Name edit field, type “Right Handed Group”

- In the Blocks to Run tab, click on the Run only the following blocks radio button

- Click on the “Left Handed Participants” checkbox to turn it off

- Click on the OK button to close the Group Editor dialog

### Using Groups

When running an experiment, you can specify which group to use when running on the fly:

When randomizing, you can specify that randomization be done on a per group basis in the following places in the program:

- In the Randomize tab of the Block Editor

- In the Randomize tab of the Trial Editor

- In the Level Selection tab of a Trial Variable Editor