After a diagonosis was done, the name of a disease is given and a medical treatment is applied. In this article it is recommended to use Mahalanobis Distance to evaluate the condition of the patient at certain intervals after the treatment. Let D02 be the initial Mahalanobis Distance and D2 be the Mahalanobis Distance at the time T elapsed, then following y may be used to see the efficiency of the treatment
y=lnD02/D2
An experimental design with minimum number of patients to compare the effectiveness of different treatments is also introduced in this article.