Bias in assignment to clinical trialsBMJ 1994; 308 doi: https://doi.org/10.1136/bmj.308.6933.920c (Published 02 April 1994) Cite this as: BMJ 1994;308:920
- J Galende,
- J Soto,
- J A Sacristan
- General Direction for Drugs and Sanitary Products, Ministry of Health, 28014 Madrid
- Clinical Research Department, Abbott Laboratories, Madrid
- Clinical Research Department, Lilly SA, Madrid.
EDITOR, - Despite the many biases to which clinical trials are subject, trials are still considered the best way to show the efficacy of a new therapeutic or prophylactic measure.1 Perhaps the most important biases are those of selection and measurement, as they most determine the validity of a study. The respective techniques of random assignment to study treatment groups and of blind experimentation are attempts to remove these biases.
We have detected a type of selection bias that does not affect the assignment of subjects in a single study to …