Automatic Biases Correction

The key point limits to define the {\it statistical model} describing the data distribution. Hence, it turns out that the characteristics related to the so-called. Inverse Tully-Fisher relation and the Direct relation are maximum likelyhood (ML) estimators of different statistical models, and we obtain coherent distance estimates as long as the same model is used for the calibration of the TF relation and for the determination of distances. The choice of the model is motivated by reasons of {\it robustness} of statistics, which depends on selection effects in observation.