Anecdotal evidence

Scientific context

In science, definitions of anecdotal evidence include:

• "casual observations/indications rather than rigorous or scientific analysis"
• "information passed along by word-of-mouth but not documented scientifically"
• "evidence that comes from an individual experience. This may be the experience of a person with an illness or the experience of a practitioner based on one or more patients outside a formal research study"
• "the report of an experience by one or more persons that is not objectively documented or an experience or outcome that occurred outside of a controlled environment"

Anecdotal evidence may be considered within the scope of scientific methods. Some anecdotal evidence can be both empirical and verifiable, e.g., case studies in medicine. Other anecdotal evidence does not qualify as scientific evidence because its nature prevents it from being investigated by the scientific method, such as folklore or intentionally fictional anecdotes. Anecdotal evidence is considered the least certain type of scientific information. Researchers may use anecdotal evidence for suggesting new hypotheses but never as validating evidence.

Anecdotal evidence varies in formality. For instance, in medicine, published anecdotal evidence by a doctor like a case report is subjected to formal peer review. Although such evidence is seen as inconclusive, researchers sometimes regard it as an invitation to more rigorous scientific study. For instance, one study found that 35 of 47 anecdotal reports of drug side effects were later sustained as "clearly correct".

Where only one or few anecdotes are presented, they risk being unreliable due to cherry-picking or otherwise non-representative sampling. Similarly, psychologists have found that due to cognitive bias, people are more likely to remember notable or unusual examples. Thus, anecdotal evidence is not necessarily representative of a typical experience even when accurate. Determination of whether an anecdote is typical requires statistical evidence. Misuse of anecdotal evidence in the form of argument from anecdote is an informal fallacy and is sometimes referred to as the "person who" fallacy, with statements like "I know a person who..." or "I know of a case where...". This places undue weight on possibly atypical experiences of close peers. If an anecdote illustrates a desired conclusion rather than a logical conclusion, it is considered a faulty generalization.

In medicine, anecdotal evidence may be subject to the placebo effect.

Legal

In the legal sphere, anecdotal evidence, if it passes certain legal requirements and is admitted as testimony, is a common form of evidence used in a court of law. In many cases, anecdotal evidence is the only evidence presented at trial.

For a testimony to be considered evidence, it must be given under oath, where the individual swears they only testify to their words and actions. Someone intentionally lying under oath is subject to perjury. However, these legal rigors do not make testimony in a court of law equal to scientific evidence. Testimony about another person's experiences or words is termed hearsay and is usually not admissible. However, hearsay that is not objected to by a judge is considered evidence for a jury. This means trials contain a considerable amount of anecdotal evidence that juries find relevant. Eyewitness testimony, a type of anecdotal evidence, is considered the most compelling form of evidence by a jury.

References

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