True regarding double blinding placebo controlled clinical trial:: (A) Some patients are not treated, (B) The clinician does not know which treatment is given to the patient, (C) 50% of the patients do not know what drug they receive, (D) Everybody receives both the drugs
Answer is B. (Refer: K. Park’s Textbook of Preventive and Social medicine, 24th edition, pg no: 78)
Bias

Any systematic error in an epidemiological study occurring during data collection, compilation, analysis and interpretation
Types of bias