<prompt> Which of the following is not true about non randomized trial?Approach of comparability highDegree of comparability highThe experiment can serve as its own control or can utilize a natural controlSeveral trials may be needed before evaluation is considered conclusive  <response>: 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. 