Occupancy data is provided by secondary sources. Surveys are conducted by telephone solicitation directly with property managers or by mailed surveys, and are adjusted by the surveying agency for known discrepancies.

Due to the difficulty of reporting absolute vacancy (the number of units vacant at a given point) - a function of reporting errors, and timing errors - data is represented as a reasonably-accurate (for-the-most-part) representation of market conditions at a point in time.