Participating in research incurs its own risk for bias in research subjects themselves. The classic Milgram studies on obedience to authority are discussed as classic studies of response bias. Methods for unbiased questionaire design, especially for sensitive topics, are reviewed. The iconic Hawthorne studies are considered and the impact of litigation on study subjects is described. Pretest sensitization occurs when preliminary screening tests for study eligibility interact with the study’s primary intervention. Informative presence bias results from research subjects having multiple contacts with the health care system from which they are recruited.