How many sales are needed for MRA to be effective?

For mass appraisal purposes, particularly when utilizing the Multiple Regression Analysis (MRA) method, a minimum number of sales is required to ensure statistical reliability and validity of the model. The effectiveness of MRA hinges on having enough data points to accurately estimate relationships between property characteristics and their sale prices.

Having 50 to 100 sales provides a robust dataset that not only captures variability in property types and locations but also helps to mitigate the risk of outliers skewing the results. This range of sales leads to a stronger statistical foundation, offering more reliable coefficients and improving the overall predictive power of the model.

In contrast, relying on too few sales would likely result in a model that is not adequately representative of the market, thereby compromising the results. A significantly larger number of sales, such as over 200, may also be beneficial, but the specified range of 50 to 100 is generally considered sufficient for effective analysis within mass appraisal frameworks.