Section 591.219 - How does OPM compute shelter price indexes?(a) In addition to rental and rental equivalence prices and/or estimates, OPM obtains for each unit surveyed information about the important characteristics of the unit, such as size, number of bathrooms, and other amenities that reflect the quality of the unit.(b) OPM then uses these characteristics and rental prices and/or estimates in hedonic regressions (a type of multiple regression) to compute for each COLA survey area the price index for rental and/or rental equivalent units of comparable quality and size between the COLA survey area and the Washington, DC, area. 67 FR 22340 , May 3, 2002, as amended at 69 FR 59763 , Oct. 6, 2004