This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
Which of the following is not true about non randomized trial? 
Select and explain. 
A. Approach of comparability high, B. Degree of comparability high, C. The experiment can serve as its own control or can utilize a natural control, D. Several trials may be needed before evaluation is considered conclusive
B: Degree of comparability high
Answer: B: Degree of comparability high 
Explanation: Ans. is 'b' i.e., Degree of comparability high Non-randomized trials o It is not always possible for ethical, administrative and other reasons to reso to a randomized controlled trial in human beings. o In such situations, non-randomized trials are used. o As there is no randomization --> degree of comparability will be low and the chances of spurious result is high. o Major types of non-randomized trials are : ? i) Uncontrolled trials ---> Control group is not used for example, effectiveness of pap test for cervical cancer. ii) Natural control (natural experiments) --3 Nature has separated the papulation in two groups for example, in respect to cigarette smoking, people have separated themsleves into two groups, smokes and non-smokers. iii) Before and after comparison study (Pre postclinical trial) These studies centre round comparing the incidence of disease before and after introduction of a preventive measures. o The events which took place prior to use of the new treatment or preventive procedure are used as a standard for comparison. o In other words, the experiment serves as its own control, this eliminates viually all group differences. o Several trials may be needed before evaluation is considered conclusive. Note : I am not sure about option 'a' as i am not able to understand this option.