<prompt> The purpose of double blinding in clinical trails is to-Achieve comparability between study and control groupsAvoid observer biasAvoid subject biasAvoid observer and subject bias  <response>: There may be bias in randomized control trials. Randomization cannot guard against these so of bias, nor the size of the sample. In order to reduce these problems, a technique known as blinding is adopted. Ref: 25th edition, Parks Textbook of Preventive and Social Medicine, Page no. 91 