Mario was attempting to develop a cure for the flu. Mario gave three test subjects, all sick with the flu, massive doses of vitamin C. All three subjects recovered within a week. Mario concluded that massive doses of vitamin C will cure the flu. Why did the scientific community deem Mario's research to be invalid?

Clinical trial of dubious quality to test his hypothesis about vitamin C; a clinical trial that other researchers rated as defective. In his research, there was not even a randomization to take vitamin C or not, it was simply observed the three who were given the micronutrient, without having a subject who was not given to compare results.