Dr. Reside treated 20 children using a new therapeutic procedure. An outside observer rated the children's activity level on a laboratory task before and after the treatment; 80% of the children decreased their activity level following treatment, and Dr. Reside concluded that the procedure was highly effective. What is the major problem with Dr. Reside’s experiment?

Dr. Reside's experiment can not be considered effective because his study has only treatment subjects group and lack of control group. That's why his study can be very good but not valid without control group.

In his study, he concluded that 80% children after therapeutic treatment decreased the activity level which can be true but not valid without control group because when he use control group in his study then we will be able to compare the normal or control group and treatment group. Then the study will be valid and effective as well.

answer; i do believe that the correct answer is ( portal of exit in the chain of transmission); good luck