METHOD-DOWN BIAS:
A bias that occurs when one discredits the importance or results of study because it uses a method which they personally disfavour1. For example, one may assume a study is not valid or poor quality because it uses an observational and/or retrospective design; despite the study being high quality.
In reality, the concepts of study design and study temporality (whether it was conducted prospectively/forward or retrospectively/backwards in time), and validity are different, and often unrelated. Such that, a study which is retrospective and observational may be higher quality, and thus more valid than a prospective experimental study (e.g. randomized controlled trial), or vice versa.
A persistent and common misconception in medical research is that there is a hierarchy of study designs; where randomized controlled trials provide the greatest validity, followed by observational studies, case–control studies, and case-studies being least valid and reliable2.
A study should be evaluated for whether the design is relevant to the question being asked, and not whether a study uses a specific design in general. If the question is to study the efficacy of a new drug, then a randomized controlled trial may be best suited for that question. However in some cases, conducting this type of study may be unethical if the drug is potentially harmful to the person taking it, or illegal. Thus, observational and retrospective studies may be the best option (an inappropriately applied prospective experimental study would be less valid than an appropriately applied retrospective observational study: e.g. we still have valid evidence that cocaine is harmful to humans from observational studies, despite having very few randomized experimental studies on its safety in humans).
Method-Down Bias is a type of Interpretive Bias, and the opposite of Method-Up Bias. Method-Down Bias may occur due to an evaluators inability to understand the process of critical appraisal of science, and/or may feel they do not need to spend the time to fully appraise a study for its scientific qualities (often it appears easier and faster to define the quality of a study based on its superficial characteristics (i.e. study design used) vs. reading and appraising an entire paper). Also see: Interpretive Bias, Disfavoured Design Bias, and Method-Up Bias.
References:
1. Earl-Slater A. The Handbook of Clinical Trials and Other Research. Abingdon: Radcliffe Medical Press Ltd. 2002. (Link to Reference)
2. Rothman KJ. Six persistent research misconceptions. J Gen Intern Med. 2014;29(7):1060-4. (Link to Reference)