A statement of the relationship between the indirect measurements taken of a proxy and the intended direct measurement that is sought. For example, the proxy hypothesis for using checked-in reservations in a Reservation Management System as a proxy for Physical Occupancy is that a space user who is checked-in to a reservation is present in the space for which that reservation applies for the entire duration of the reservation.

Each proxy may have multiple, possibly conflicting, hypotheses. For example, an alternative hypothesis for using checked-in reservations as a proxy for Physical Occupancy might be that a space user who is checked-in to a reservation is present in the building containing the space for which that reservation applies for at least some of the day on which the reservation is held. See Measurement and Error detection and correction for further details.