There are two temporal attributes: Occurrence (O), the number of days in a year the behavior setting is capable of occurring, and Duration (D), the number of hours the behavior setting functions during a year. Population (P) is the number of different persons who inhabit the behavior setting during the year. These three basic attributes allow for a calculation of Occupancy Time (OT), the number of person-hours spent in the behavior setting. It is the product of the occurrences (O), the average number of inhabitants per occurrence (P/O), and the average duration per occurrence (D/O).