View source for Anecdotal evidence

{{short description|Evidence relying on personal testimony}}
'''Anecdotal evidence''' is evidence based only on personal observation, collected in a casual or non-systematic manner. 

When used in [[Finance:Advertising|advertising]] or promotion of a product, service, or idea, anecdotal reports are often called a testimonial, which are highly regulated<ref>{{cite web|url = https://www.ftc.gov/sites/default/files/attachments/press-releases/ftc-publishes-final-guides-governing-endorsements-testimonials/091005revisedendorsementguides.pdf |title = Guides Concerning the Use of Endorsements and Testimonials in Advertising|publisher = FTC.gov}}</ref> in some jurisdictions.

When compared to other types of evidence, anecdotal evidence is generally regarded as limited in value due to a number of potential weaknesses, but may be considered within the scope of [[Scientific method|scientific method]] as some anecdotal evidence can be both empirical and verifiable, e.g. in the use of case studies in medicine. Other anecdotal evidence, however, does not qualify as [[Scientific evidence|scientific evidence]], because its nature prevents it from being investigated by the scientific method. Where only one or a few anecdotes are presented, there is a larger chance that they may be unreliable due to [[Cherry picking|cherry-picked]] or otherwise [[Sampling (statistics)|non-representative]] samples of typical cases.<ref name="weiten">{{cite book|page = 75 |title= Psychology: Themes and Variations|first=Wayne|last= Weiten|publisher = Wadsworth/Cengage Learning|date = 2010|isbn = 9780495601975}}</ref><ref>{{cite book|url = https://books.google.com/books?id=eNsVUGTMcDoC&pg=PA25|page= 25 |title= Research in Psychology: Methods and Design|first = C. James|last = Goodwin|publisher = John Wiley & Sons|date= 2009|isbn= 9780470522783}}</ref> Similarly, psychologists have found that due to [[Philosophy:Cognitive bias|cognitive bias]] people are more likely to remember notable or unusual examples rather than typical examples.<ref>{{cite journal |last1=Gibson |first1=Rhonda |last2=Zillman |first2=Dolf |year=1994 |title=Exaggerated Versus Representative Exemplification in News Reports: Perception of Issues and Personal Consequences |journal=Communication Research |volume=21 |issue=5 |pages=603–624 |doi=10.1177/009365094021005003 |s2cid=145050644 }}</ref> Thus, even when accurate, anecdotal evidence is not necessarily representative of a typical experience. Accurate determination of whether an anecdote is typical requires statistical evidence.<ref>{{cite web |last1=Schwarcz |first1=Joe |last2=Barrett |first2=Stephen |url=http://www.quackwatch.org/01QuackeryRelatedTopics/science.html |archive-url=https://web.archive.org/web/20120920043202/http://www.quackwatch.org/01QuackeryRelatedTopics/science.html |archive-date=20 September 2012 |access-date=16 June 2022 |title=Some Notes on the Nature of Science |url-status=unfit}}{{cbignore}}</ref> Misuse of anecdotal evidence in the form of [[Philosophy:Argument from anecdote|argument from anecdote]] is an [[Informal fallacy|informal fallacy]]<ref>{{Cite web|url=https://www.iep.utm.edu/fallacy/#AnecdotalEvidence|title=Fallacies {{!}} Internet Encyclopedia of Philosophy|website=www.iep.utm.edu|access-date=2020-04-07}}</ref> and is sometimes referred to as the "person who" fallacy ("I know a person who..."; "I know of a case where..." etc.) which places undue weight on experiences of close peers which may not be typical.

== Scientific context ==
In science, definitions of anecdotal evidence include:

* "casual observations or indications rather than rigorous or scientific analysis"<ref name="yourdictionary">{{cite web|url =https://www.yourdictionary.com/anecdotal|website = YourDictionary.com|title = anecdotal|access-date = 17 June 2019}}</ref>
* "information passed along by word-of-mouth but not documented scientifically"<ref>{{Cite web|url=https://www.nechakowhitesturgeon.org/glossary|title=Nechako White Sturgeon Recovery Initiative - Glossary - NWSRI|website=www.nechakowhitesturgeon.org|access-date=2020-04-07}}</ref>
*"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."<ref>{{Cite web|url=https://www.ncbi.nlm.nih.gov/books/NBK63658/def-item/glossary.gl1-d4/|title=Anecdotal evidence - Smart Health Choices - NCBI Bookshelf|website=www.ncbi.nlm.nih.gov|access-date=2020-04-07}}</ref>
*"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"<ref>{{Cite web|url=https://theness.com/neurologicablog/index.php/no-love-for-anecdotal-evidence/|title=No Love for Anecdotal Evidence|date=2007-03-08|website=NeuroLogica Blog|access-date=2020-04-07}}</ref>

Anecdotal evidence can have varying degrees of formality. For instance, in medicine, published anecdotal evidence by a trained observer (a doctor) is called a [[Medicine:Case report|case report]], and is subjected to formal peer review.<ref name="Jenicek">{{cite book |last= Jenicek |first= M. |title= Clinical Case Reporting in Evidence-Based Medicine |location= Oxford |publisher= Butterworth–Heinemann |year= 1999 |pages= 117 |isbn= 0-7506-4592-X }}</ref> Although such evidence is not seen as conclusive, researchers may sometimes regard it as an invitation to more rigorous scientific study of the phenomenon in question.<ref name="Vandenbroucke">{{cite journal |last= Vandenbroucke |first= J. P. |year= 2001 |title= In Defense of Case Reports and Case Series |journal= Annals of Internal Medicine |volume= 134 |issue= 4 |pages= 330–334 |pmid= 11182844 |doi= 10.7326/0003-4819-134-4-200102200-00017|s2cid= 867759 }}</ref> For instance, one study found that 35 of 47 anecdotal reports of drug side-effects were later sustained as "clearly correct."<ref name="Venning">{{cite journal |last= Venning |first= G. R. |title= Validity of anecdotal reports of suspected adverse drug reactions: the problem of false alarms |journal= Br Med J (Clin Res Ed) |year= 1982 |volume= 284 |issue= 6311 |pages= 249–52 |pmid= 0006799125 |doi= 10.1136/bmj.284.6311.249 |pmc= 1495801}}</ref>

Anecdotal evidence is considered the least certain type of scientific information.<ref name="isbn0-12-588560-1">{{cite book |author= Riffenburgh, R. H. |title= Statistics in Medicine |publisher= Academic Press |location= Boston |year= 1999 |pages= [https://archive.org/details/statisticsinmedi00riff/page/196 196] |isbn= 0-12-588560-1 |url= https://archive.org/details/statisticsinmedi00riff/page/196 }}</ref> Researchers may use anecdotal evidence for suggesting new [[Hypothesis|hypotheses]], but never as validating evidence.<ref>{{cite book | last1 = Lilienfeld | first1 = Scott O. |  last2 = Lynn | first2 = Steven Jay | last3 = Lohr | first3 = Jeffrey M. | chapter = Initial Thoughts, Reflections, and Considerations | title = Science and Pseudoscience in Clinical Psychology | chapter-url = https://books.google.com/books?id=q50gBQAAQBAJ&pg=PA9 | edition = 2 | location = New York | publisher = Guilford Publications | date = 2014 | page = 9 | isbn = 9781462517510 | quote = Testimonial and anecdotal evidence can be quite useful in the early stages of scientific investigation. Nevertheless, such evidence is almost always much more helpful in the context of discovery (i.e., hypothesis generation) than in the context of justification (i.e., hypothesis testing [...]).}}</ref><ref name="Mebius">{{cite journal |last= Mebius |first= A. |year= 2022 |title= Against 'instantaneous' expertise |journal= Philosophy, Ethics, and Humanities in Medicine |volume= 17 |issue= 11 |page= 11 |doi= 10.1186/s13010-022-00123-3 |pmid= 36127693 |pmc= 9490894 |s2cid= 252384889 |doi-access= free }}</ref>

If an anecdote illustrates a desired conclusion rather than a logical conclusion, it is considered a [[Faulty generalization|faulty]] or hasty generalization.<ref name="Thompson">Thompson B. [http://www.cuyamaca.edu/bruce.thompson/Fallacies/anecdotal.asp Fallacies.] {{webarchive |url= https://web.archive.org/web/20060420154531/http://www.cuyamaca.edu/bruce.thompson/Fallacies/anecdotal.asp |date= April 20, 2006 }}</ref> 

In any case where some factor affects the probability of an outcome, rather than uniquely determining it, selected individual cases to prove nothing; e.g. "my grandfather smoked two packs a day until he died at 90" and "my sister never smoked but died of lung cancer". Anecdotes often refer to the exception, rather than the rule: "Anecdotes are useless precisely because they may point to idiosyncratic responses."<ref>{{cite journal | first= Scott H. |last= Sicherer |title= Food allergy: When and how to perform oral food challenges |journal= Pediatric Allergy and Immunology |year= 1999 |volume= 10 |issue= 4 |pages= 226–234 |doi= 10.1034/j.1399-3038.1999.00040.x |pmid= 10678717 |s2cid= 1484234 }}</ref>

In medicine, anecdotal evidence is also subject to placebo effects.<ref name="Lee">{{Cite web|url=https://www.medicinenet.com/evaluating_medications_and_supplement_products/views.htm|title=Evaluating Treatment Products|website=MedicineNet}}<!-- old archived link was https://archive.today/20121209111018/http://www.medicinenet.com/script/main/art.asp?articlekey=55090&page=2 --></ref>

==See also==
{{Div col}}
* {{annotated link|Finance:Anecdotal value}}
* {{annotated link|Philosophy:Argument from ignorance}}
* {{annotated link|Confirmation bias}}
* {{annotated link|Correlation does not imply causation}}
* {{annotated link|Empirical evidence}}
* {{annotated link|Philosophy:Eyewitness testimony}}
* {{annotated link|Fallacy}}
* {{annotated link|Faulty generalization}}
* {{annotated link|Lived experience}}
* {{annotated link|Philosophy:Post hoc ergo propter hoc}}
* {{annotated link|Social:Presumption of guilt}}
* {{annotated link|Scientific method}}

{{Div col end}}

==References==
{{reflist}}

{{Fallacies}}

[[Category:Informal fallacies]]
[[Category:Philosophy of science]]
[[Category:Skepticism]]
[[Category:Evidence]]
[[Category:Inductive fallacies]]
[[Category:Pseudoscience]]

{{Sourceattribution|Anecdotal evidence}}