<prompt> In a randomized controlled trial, the essential purpose of randomization is -To produce double blindingTo decrease the follow- up periodTo eliminate the selection biasTo decrease the sample size  <response>: Ans. is c i.e., To eliminate the selection bias o Experimental studies are of two types ? i Randomized controlled trials ii Non - Randomized Randomized controlled trials RCT o Randomization is the hea of RCT. o Randomization is a statistical procedure by which the paicipants are allocated into study group in which intervention is given and control group reference group in which intervention is not given. o It is woh noting that randomisation is done while dividing the paicipants into study group and control reference group, and not while selecting subjects for study, i.e. randomization is done after the sample of subjects has already been selected. o Therefor, each paicipant has equal and known chance of falling into either study group or control group. o Randomization is an attempt to eliminate bias and allow comparability. o It will give the greatest confidence that the groups are comparable so that like can be compared with like. o It ensures that the investigator has no control over allocation of paicipants to either study or control group, thus eliminating what is known as selection bias. o That means, by random allocation, every individual gets an equal chance of being allocated into either group, study experimental group or control reference group. o Unit of study in RCT: Patient o RCT is of two types: Concurrent parallel design: Comparisons are made between 2 groups: 1 Experimental group: Is exposed to specific medication or intervention 2 Reference group: Is not exposed to specific medication or intervention Crossover design: Comparisons are made between 2 groups: 1 Experimental group: Is exposed to specific medication or intervention Reference group: Is not exposed to specific medication or intervention Then the groups are crossed-over exposed group now becomes non-exposed and vice-versa. 