Mass Appraisal

Maine assessors use a valuation methodology called mass appraisal. In mass appraisal we build a database of sales by collecting recently sold properties into like groupings. The largest group is the entire town. Then we divide the entire town into three sub-groups: residential properties, commercial properties and land.

We continue dividing into more and more finely detailed groupings until we no longer have enough sales with which we can make useful conclusions. For example, we further divide residential properties into single-family, multi-unit, mobile homes, condos and timeshares. We break each of these groups into waterfront and non-waterfront. We break down waterfront into salt and freshwater. And so on.

We come to valuation conclusions by applying basic statistical analysis techniques to discover the central tendencies within each grouping. Central tendencies are the median average, the mean average and weighted mean average. In assessing, we lean most heavily on the median average because it is less affected by outlier sales.