As part of the reappraisal process the Assessor analyzes all sales that occur within a specific data gathering period. Depending on sales volume this period may stretch back as far as 60 months prior to the statutory appraisal date. Often, market conditions will change during this time frame. For example, increasing demand for single family residences may cause their sales prices to increase over time.
The Assessor is required to study these market changes and to adjust older sales to account for them. Each sale is adjusted based on how the market changed between the actual sale date and the appraisal date. These time adjustments can be positive (improving market conditions) or negative (deteriorating market conditions), and can vary with the type of property and area of the county. The process is referred to as time trending, and the resulting time adjusted sales prices (TASP) represent what each property would have sold for if it had sold on the appraisal date.
This approach to time trending is a standard appraisal practice used throughout the world, and is recommended by the International Association of Assessment Officers.