ALLEGIANCE BIAS:
When the results of a study are contaminated, or distorted by a scientist’s preferred method of conducting the study, or preferred method of treatment used1,2. Or generally, when a study is biased due to a researcher’s allegiance (i.e. loyalty/commitment) to a school of thought.
In the context of medical science, Allegiance Bias is a type of Academic Bias, that is relevant to studies within the social sciences and psychotherapy. It is similar to Method-Up Bias. However, Allegiance Bias may occur, in some form, in any study when a scientist, who is responsible for interpreting the results, is directly involved in administering the treatment or exposure of interest. Blinding of study personnel to exposure administration, and outcome measurement may help to mitigate Allegiance Bias in some contexts. Also see: Academic Bias, Method-Up Bias, Favoured Design Bias, and Bias Due to Conflicts of Interest.
References:
1. Wilson GT, Wilfley DE, Agras WS, Bryson SW. Allegiance Bias and Therapist Effects: Results of a Randomized Controlled Trial of Binge Eating Disorder. Clin Psychol (New York). 2011 Jun;18(2):119-125. (Link to Reference)
2. Schünemann O, Jansen A, Willutzki U, Heinrichs N. Allegiance Bias and Treatment Quality as Moderators of the Effectiveness of Humanistic Psychotherapy: Protocol for a Systematic Review and Meta-Analysis. JMIR Res Protoc. 2019 Nov 25;8(11):e15140. (Link to Reference)