The use of available data from public records(sales/listing prices/rental prices, etc.) to approximate value. Their error rate can be close when homes are similar, as with small lot and house size's such as properties in the outer borough's of Manhattan, and Nassau County or developments in outlying area's. However, the error rate is much higher, say 7.5%+ when they are off-the-market such as on the east end of Long Island. This can amount to tens of thousand's of dollars when the median price range in the towns of Southold, Riverhead, Southampton, Easthampton and Shelter Island are certainly more than One-half Million to well over One Million $$$$$. Can YOU afford not to have a NYS Certified Appraiser provide you with more specific analysis of your market and determine what's overpriced and underpriced. Call or text us at 631.513.0442.