According to State statute, the assessor is required to gather and confirm sales within an 18-month period ending on the June 30 of the year prior to a reappraisal year. This data-gathering period is referred to as the sales study period. While statute prescribes an 18-month study period, assessors are allowed to extend the study period back in time in six-month increments up to 60 months to ensure enough qualified sales within each economic area. When sales volume is high, fewer years can be used. When sales volume is low, more years may be necessary to obtain adequate comparable valuation data.