Computer-Assisted Mass Appraisal System ( CAMA )

In order to calculate the appraised value of 400,000 parcels of property in St. Louis County, the St. Louis County Assessor’s office uses a computerized software package written by an external vendor, referred to as the Computer-Assisted Mass Appraisal system, or CAMA.  The system uses the property information provided to it by the County and puts it thru a series of complicated (albeit seemingly unknown) algorithms in order to calculate the appraised value. 

Source:  https://stlouisco.com/portals/8/docs/document%20library/assessor/Brochures/ReassessmentBasics2017.pdf

If you ask anyone at the County office, that’s what they’ll tell you.  But that’s all they’ll tell you.  If you ask for anything more, like for specifics about how their “Statistical Model Value” on the "Assessor's Comparable Sales" list is calculated, they’ll tell you that they don’t know, that it’s in the code, and even if they did know, they couldn’t tell you because that information is proprietary.

The software tool used by the STL County Assessor’s office is a package named iasWorld offered by the software development company, Tyler Technologies.  See https://www.tylertech.com.  They have offered mass appraisal software for years and boast having hundreds of clients throughout the U.S. and beyond. 

Since I couldn’t get any answers from the St. Louis County Assessor’s office regarding how the numbers were calculated, I attempted to get some questions answered by contacting Tyler Technologies, directly.  Certainly, they would know how the values were calculated, right? 

At first, they were very friendly and responsive, presumably mistakenly thinking that I was inquiring as a potential new client.   But when I explained that I wasn’t in the market for software and simply wanted to get some answers to questions regarding the calculation of my property assessment for my appeal pending with St. Louis County, they declined any further discussion and re-directed me back to the St. Louis County Assessor’s office.

What’s the big mystery?  Why the secrecy?  Especially since both the County Assessor’s office and the CAMA software are supposedly using “generally accepted appraisal techniques.”  How can "generally accepted appraisal techniques" be proprietary?