What does the evaluation of the house I want to sell or buy with … the Gauss curve have to do with it? Agree, the Gaussian curve (Gaussian) is certainly a particularly advanced mathematical concept … but still with significant implications with the real world and, specifically, in the real estate appraisal. For those who wish to have fun analyzing the real estate sale from a mathematical point of view, they can choose to deepen the theories of the German Karl Friedrich Gauss. In fact, he demonstrated that under suitable hypotheses, the distribution of certain phenomena tends to resemble the normal distribution, in fact the Gauss distribution is often called normal. The adjective is significant because it indicates that many phenomena can be described by a Gaussian or Gauss-like curve. If it is true that Gaussian applies to an infinite population of measurements and to completely random events, it is also true that bell curves can easily describe many phenomena; for these phenomena also the concepts of mean and standard deviation continue to be valid, even if often only the former can be defined with considerable precision.

Principle of ordinariness. In summary, it could be said that normal is a borderline case for many situations. Mathematicians know perfectly well that the borderline case is not the actual situation, but they use it to grasp the elements common to multiple situations, interpreting Gauss’s theorem as a useful simplification. The principle of ordinariness consists in referring to average conditions, normal according to the Gauss distribution (the bell curve). Ordinary value, statistically has the greatest probability of occurring in reality. The principle of ordinariness is expressed in three criteria.

1. Statistical criterion. From an estimative point of view, it means asserting that, having fixed the evaluation criterion and the intended use, the most probable estimate value of a property is the average value of the normal (or Gaussian) statistical distribution of the estimate values. According to this distribution, the estimate value is the most frequent central value.

2. Economic criterion. Concerns the identification of the destination that configures the highest and best use (HBU), i.e. the maximum and best use of the property.

3. Legal criterion. It is based on legal rules and concerns particular conventional estimates defined by the legislator according to particular rules and criteria. These are estimates required by the public administration. In analytical chemistry it is the probability curve that has the maximum at the true value, and then progressively decreases on the right and left sides of the true value (Cartesian graph). In general, the Gaussian curve is the distribution curve of the values of many measurements, if the number of these measurements tends to infinity, and is bell-shaped, as we move away from the true value, i.e. the maximum peak of the bell , the values tend to zero.