<prompt> True regarding double blinding placebo controlled clinical trial:Some patients are not treatedThe clinician does not know which treatment is given to the patient50 of the patients do not know what drug they receiveEverybody receives both the drugs  <response>: Refer: K. Parks Textbook of Preventive and Social medicine, 24th edition, pg no: 78BiasAny systematic error in an epidemiological study occurring during data collection, compilation, analysis and interpretationTypes of bias 