 Methodological errors such as poor blinding or poor randomisation allow factors such as the placebo effect or selection bias to adversely affect the results of a trial.Randomisation is a process to remove potential distortion of statistical results arising from the manner in which the
trial is conducted, in particular in the selection of subjects.Studies have indicated, for example, that nonrandomised trials are more likely to show a positive result for a new treatment than for an established conventional one.