1. A method of detection of fraud in a claim of valuation, such as an appraisal or a mortgage application for purchase, loan, or refinance of a subject real property to be used as collateral for the mortgage, using a computer system, the method comprising the steps of: maintaining a database of sales prices in the computer system of a plurality of real properties in a geographic area in which the subject real property is located, obtaining from the computer system valuation history data for the subject property; obtaining, using the computer system, historical sales data for property in the geographic area in which the subject real property is located, computing price ratio data using the valuation history for the subject property and the historical sales data for the subject property in the geographic area in which the subject property is located, and computing a distortion index based on the price ratio data to detect fraud in the mortgage application.