Independent Variables and Participant Groups

Tobii Pro Studio

Learn more about how to define independent variables and create participant groups for filtering data in Tobii Pro Studio.

Tobii Studio screenshot

Tobii Pro Studio provides a very useful capability for organizing study participants and as an aid for carrying out analyses on subgroups of participants. These two related functions are Independent Variables and Participant Groups.

Independent Variables (IV) can be thought of in the orthodox sense of an experimental condition that is manipulated. It can also be considered, more generally, as a sorting variable. Examples of IVs could be sex, age range, dominant hand, geographic location, income level, or literacy status. As long as the dimension can be listed as discrete categories, you can input them as IVs. This is covered in the Pro Studio manual section 4.2.2. Create your entries by selecting the Independent Variables item under the Tools menu. In the following example, an IV is created for age of the subject, AgeRange, with the possible values of 18-23, 24-29, and 30-34. LowLiteracy is set up to capture subjects’ low literacy status and is dichotomized as Yes or No. Finally, Male and Female are entered as options for the IV Sex.

While IVs can be created here and entered either before or after the subject has actually been tested, there is another way to create and populate IV data. When you include a questionnaire element in the study timeline, each questionnaire item spawns an IV and each response populates the value field with the selected response option (Pro Studio manual section Thus, if a subject is asked to choose their favorite gaming console from the options WiiU, XBOX, or PS4, clicking on the associated radio button will record that value for them in the IV named GameConsole.

However you do it, the creation of Independent Variables sets you up to make use of the Participant Groups (PG) functionality (section 7.2.1). In essence, PGs allow the analyst to slice and dice the total pool of study subjects into subgroups to create comparisons and contrasts when viewing gaze data visualizations or calculating metrics. Let’s see how this works. In the following screen shot, I’ve created nine subjects and populated their IVs. You can see that we have subjects with all possible combinations of the three IVs that we previously created. Now we’re ready to create some participant groups. Note: The values for the independent variables can be edited at any time, which is a helpful capability, especially in the case that a subject makes an unintended or incorrect selection on a questionnaire item.

Tobii Studio screenshot

You can create participant groups in the Visualizations or Statistics tabs in Pro Studio. Since the operation is identical in both places, let’s do it in the Statistics tab for this example. In the next screenshot, I’ve clicked on the Participant Group drop-down. Since we haven’t created any yet, the default option “All Participants” is selected. When you click on “Create new participant group” you are then presented with a popup window where you can select one or more response options for each of the IVs to create a profile for the group.

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