(A) To minimise the selection bias # Randomized controlled trial (RCT) is a scientific procedure most commonly used in testing medicines or medical procedures.> RCTs are considered the most reliable form of scientific evidence because it eliminates all forms of spurious causality.> RCTs are mainly used in clinical studies, but are also employed in other sectors such as judicial, educational, social research.> Clinical RCTs involve allocating treatments to subjects at random.> This ensures that the different treatment groups are 'statistically equivalent'.> There are a couple of statistical issues to consider in generating the randomization sequences :> Balance: since most statistical tests are most powerful when the groups being compared have equal sizes, it is desirable for the randomization procedure to generate similarly-sized groups.> Selection bias: depending on the amount of structure in the randomization procedure, investigators may be able to infer the next group assignment by guessing which of the groups has been assigned the least up to that point.> This breaks allocation concealment and can lead to bias in the selection of patients for enrollement in the study. But compared to other studies randomized control studies minimises this bias.> Accidental bias: if important covariates that are related to the outcome are ignored in the statistical analysis, estimates arising from that analysis may be biased.> Potential magnitude of that bias, if any, will depend on the randomization procedure.