Mass Appraisal

Understanding Mass Appraisal

Colorado State Statutes [39-1-103 (5) (a) and (8) (a)] require all county assessors to value residential real property solely by the market approach. There are several methods used to determine values by the market: Multiple Regression, Paired Sales and Market-Adjusted Cost Approach.

Multiple Regression Analysis Method

Multiple Regression explores and quantifies the relationship between two or more components of known and available data (sale prices and property characteristics) to generate a market value. In essence this methodology uses aspects of both the paired sales and cost approach methodologies by determining which property characteristics are the primary contributors (Cost approach) and the amount they contribute (Paired sales).
Regression does not require strict similarity between property sales because it estimates the value contribution (coefficient) for each attribute using a “goodness of fit” or error-minimizing technique. This methodology produces statistics about the quality of the attribute contribution that the other methods cannot provide. These statistics help evaluate the predictive accuracy of the regression equation, or essentially, the ability to predict sales price.

Value Models

The value models used for Boulder County are the result of many MRA iterations. We review the data on a county-wide basis to review market trends. We also review the value models used in previous reappraisals for trends and consistency. Each economic area and property type (Single Family, Condo, Manufactured Home) have different value models. Before values are finalized, we review each neighborhood for any uniqueness that is not handled with the economic area value model. We test for statistical compliance and equitable valuation. Overall, the goal is to provide a value model that best reflects market value.

Contact Us


Phone: 303-441-3530
Fax: 303-441-4996


Mailing Address

PO Box 471
Boulder, CO 80306-0471

Hours: 7:30 a.m. to 5 p.m.
Closed Friday


Assessor Boulder and Longmont Drop Boxes


1325 Pearl St., 2nd floor
Boulder, CO 80302
Hours: 7:30 a.m. to 5 p.m.
Map and Directions Boulder Location


515 Coffman St., Suite 114
Hours: 7:30 a.m. to 5 p.m.
Monday only
Map and Directions Longmont Location


1755 S Public Road
Hours: 7:30 a.m. to 5 p.m.
Tuesday only
Map and Directions Lafayette Location