True about simple randomization is: March 2011
Correct Answer: Every person has an equal chance of selection
Description: Ans. A: Every person has an equal chance of selection In simple random sampling, every unit of population has equal chances of being selected Randomized controlled trial (RCT) It is a type of scientific experiment - a form of clinical trial - most commonly used in testing the safety (or more specifically, information about adverse drug reactions and adverse effects of other treatments) and efficacy or effectiveness of healthcare services (such as medicine or nursing) or health technologies (such as pharmaceuticals, medical devices or surgery). The key distinguishing feature of the usual RCT is that study subjects, after assessment of eligibility and recruitment, but before the intervention to be studied begins, are randomly allocated to receive one or other of the alternative treatments under study. Random allocation in real trials is complex, but conceptually, the process is like tossing a coin. After randomization, the two (or more) groups of subjects are followed up in exactly the same way, and the only differences between the care they receive, for example, in terms of procedures, tests, outpatient visits, follow-up calls etc. should be those intrinsic to the treatments being compared. The most impoant advantage of proper randomization is that it minimizes allocation bias, balancing both known and unknown prognostic factors, in the assignment of treatments." The advantages of proper randomization in RCTs include: "It eliminates bias in treatment assignment," specifically selection bias and confounding. "It facilitates blinding (masking) of the identity of treatments from investigators, paicipants, and assessors." "It permits the use of probability theory to express the likelihood that any difference in outcome between treatment groups merely indicates chance. There are two processes involved in randomizing patients to different interventions. First is choosing a randomization procedure to generate an unpredictable sequence of allocations; this may be a simple random assignment of patients to any of the groups at equal probabilities, may be "restricted," or may be "adaptive." A second and more practical issue is allocation concealment, which refers to the stringent precautions taken to ensure that the group assignment of patients are not revealed prior to definitively allocating them to their respective groups. Non-random "systematic" methods of group assignment, such as alternating subjects between one group and the other, can cause "limitless contamination possibilities" and can cause a breach of allocation concealment. Randomization procedures An ideal randomization procedure would achieve the following goals: Equal group sizes for adequate statistical power, especially in subgroup analyses. Low selection bias. That is, the procedure should not allow an investigator to predict the next subject's group assignment by examining which group has been assigned the fewest subjects up to that point. Low probability of confounding (i.e., a low probability of "accidental bias"), which implies a balance in covariates across groups. Simple randomization: This is a commonly used and intuitive procedure, similar to "repeated fair coin-tossing." Also known as "complete" or "unrestricted" randomization, it is robust against both selection and accidental biases. However, its main drawback is the possibility of imbalanced group sizes in small RCTs. It is therefore recommended only for RCTs with over 200 subjects. Restricted randomization: To balance group sizes in smaller RCTs, some form of "restricted" randomization is recommended. The major types of restricted randomization used in RCTs are: Permuted-block randomization or blocked randomization: a "block size" and "allocation ratio" (number of subjects in one group versus the other group) are specified, and subjects are allocated randomly within each block. Adaptive biased-coin randomization methods (of which urn randomization is the most widely-known type)
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