Respondent activities are recorded as six-digit numbers (ACTIVITY). The first two digits correspond to a broad category, the middle two to a more detailed subcategory, and the final two to a specific activity within those categories. Users may select any combination of activities from the activity hierarchy to create time use variables.

For example, broad category 02 refers to "Household Activities." Within "Household Activities," subcategory 01 refers to "Housework." Within that subcategory, 02 refers to "Doing laundry." The full six digit code for "Doing laundry" is therefore 020102.