Thursday, 7 January 2016

Anecdotal Evidence

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Anecdotal evidence is evidence from anecdotes. Where only one or a few anecdotes are presented, there is a larger chance that they may be unreliable due to cherry-picked or otherwise non-representative samples of typical cases.[1][2] Anecdotal evidence is considered dubious support of a generalized claim; it is, however, within the scope of scientific method for claims regarding particular instances, for example the use of case studies in medicine.
The term is often used in contrast to scientific evidence, such as evidence-based medicine, which are types of formal accounts.[citation needed] Some anecdotal evidence does not qualify as scientific evidence because its nature prevents it from being investigated using the scientific method. Misuse of anecdotal evidence is an informal fallacy and is sometimes referred to as the "person who" fallacy ("I know a person who..."; "I know of a case where..." etc. Compare with hasty generalization). Anecdotal evidence is not necessarily representative of a "typical" experience; in fact, human cognitive biases such as confirmation bias mean that exceptional or confirmatory anecdotes are much more likely to be remembered. Accurate determination of whether an anecdote is "typical" requires statistical evidence.[3][4]
The term is sometimes used in a legal context to describe certain kinds of testimony. Psychologists have found that people are more likely to remember notable examples than typical examples.[5] When used in advertising or promotion of a product, service, or idea, anecdotal reports are often called a testimonial, which are banned in some[which?] jurisdictions.[citation needed]


In all forms of anecdotal evidence, its reliability by objective independent assessment may be in doubt. This is a consequence of the informal way the information is gathered, documented, presented, or any combination of the three. The term is often used to describe evidence for which there is an absence of documentation, leaving verification dependent on the credibility of the party presenting the evidence.

Scientific context[edit]

In science, definitions of anecdotal evidence include:
  • "casual observations or indications rather than rigorous or scientific analysis"[6]
  • "information passed along by word-of-mouth but not documented scientifically"[citation needed]
Anecdotal evidence can have varying degrees of formality. For instance, in medicine, published anecdotal evidence by a trained observer (a doctor) is called a case report, and is subjected to formal peer review.[7] Although such evidence is not seen as conclusive, it is sometimes regarded as an invitation to more rigorous scientific study of the phenomenon in question.[8] For instance, one study found that 35 of 47 anecdotal reports of drug side-effects were later sustained as "clearly correct."[9]
Anecdotal evidence is considered the least certain type of scientific information.[10] Researchers may use anecdotal evidence for suggesting new hypotheses, but never as validating evidence.

Faulty logic[edit]

Anecdotal evidence is often unscientific or pseudoscientific because various forms of cognitive bias may affect the collection or presentation of evidence. For instance, someone who claims to have had an encounter with a supernatural being or alien may present a very vivid story, but this is not falsifiable. This phenomenon can also happen to large groups of people through subjective validation.
Anecdotal evidence is also frequently misinterpreted via the availability heuristic, which leads to an overestimation of prevalence. Where a cause can be easily linked to an effect, people overestimate the likelihood of the cause having that effect (availability). In particular, vivid, emotionally charged anecdotes seem more plausible, and are given greater weight. A related issue is that it is usually impossible to assess for every piece of anecdotal evidence, the rate of people not reporting that anecdotal evidence in the population.
A common way anecdotal evidence becomes unscientific is through fallacious reasoning such as the Post hoc ergo propter hoc fallacy, the human tendency to assume that if one event happens after another, then the first must be the cause of the second. Another fallacy involves inductive reasoning. For instance, if an anecdote illustrates a desired conclusion rather than a logical conclusion, it is considered a faulty or hasty generalization.[11] For example, here is anecdotal evidence presented as proof of a desired conclusion:
There's abundant proof that drinking water cures cancer. Just last week I read about a girl who was dying of cancer. After drinking water she was cured.
Anecdotes like this do not prove anything.[12] In any case where some factor affects the probability of an outcome, rather than uniquely determining it, selected individual cases prove nothing; e.g. "my grandfather smoked 40 a day until he died at 90" and "my sister never went near anyone who 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."[13]
More generally, a statistical correlation between things does not in itself prove that one causes the other (a causal link). A study found that television viewing was strongly correlated with sugar consumption, but this does not prove that viewing causes sugar intake (or vice versa).
In medicine anecdotal evidence is also subject to placebo effects:[14] it is well-established that a patient's (or doctor's) expectation can genuinely change the outcome of treatment. Only double-blind randomized placebo-controlled clinical trials can confirm a hypothesis about the effectiveness of a treatment independently of expectations.
By contrast, in science and logic, the "relative strength of an explanation" is based upon its ability to be tested, proven to be due to the stated cause, and verified under neutral conditions in a manner that other researchers will agree has been performed competently, and can check for themselves.


Witness testimony is a common form of evidence in law, and law has mechanisms to test witness evidence for reliability or credibility. Legal processes for the taking and assessment of evidence are formalized. Some witness testimony may be described as anecdotal evidence, such as individual stories of harassment as part of a class action lawsuit. However, witness testimony can be tested and assessed for reliability. Examples of approaches to testing and assessment include the use of questioning, evidence of corroborating witnesses, documents, video and forensic evidence. Where a court lacks suitable means to test and assess testimony of a particular witness, such as the absence of forms of corroboration or substantiation, it may afford that testimony limited or no "weight" when making a decision on the facts.

Scientific evidence as legal evidence[edit]

In certain situations, scientific evidence presented in court must also meet the legal requirements for evidence. For instance, in the United States, expert testimony of witnesses must meet the Daubert standard. This ruling holds that before evidence is presented to witnesses by experts, the methodology must be "generally accepted" among scientists. In some situations, anecdotal evidence may meet this threshold (such as certain case reports which corroborate or refute other evidence).
Altman and Bland argue that the case report or statistical outlier cannot be dismissed as having no weight: "With rare and uncommonly occurring diseases, a nonsignificant finding in a randomized trial does not necessarily mean that there is no causal association between the agent in question and the disease."[15]

See also[edit]


  1. Jump up ^ p. 75 of Psychology: Themes and Variations by Wayne Weiten
  2. Jump up ^ p. 25 in Research in Psychology: Methods and Design, by C. James Goodwin.
  3. Jump up ^ Schwarz J, Barrett S. Some Notes on the Nature of Evidence.Link. Retrieved 26 August 2012. "Anecdotal evidence is unreliable, because positive results are much more likely to be reported than negative ones."
  4. Jump up ^ Introduction to Statistical Inference section 1.1. Link.
  5. Jump up ^ Gibson, Rhonda; Zillman, Dolf (1994). "Exaggerated Versus Representative Exemplification in News Reports: Perception of Issues and Personal Consequences". Communication Research 21 (5): 603–624. doi:10.1177/009365094021005003. 
  6. Jump up ^
  7. Jump up ^ Jenicek, M. (1999). Clinical Case Reporting in Evidence-Based Medicine. Oxford: Butterworth–Heinemann. p. 117. ISBN 0-7506-4592-X. 
  8. Jump up ^ Vandenbroucke, J. P. (2001). "In Defense of Case Reports and Case Series". Annals of Internal Medicine 134 (4): 330–334. doi:10.7326/0003-4819-134-4-200102200-00017. PMID 11182844. 
  9. Jump up ^ Venning, G. R. (1982). "Validity of anecdotal reports of suspected adverse drug reactions: the problem of false alarms". Br Med J (Clin Res Ed) 284 (6311): 249–52. doi:10.1136/bmj.284.6311.249. PMC 1495801. PMID 0006799125. 
  10. Jump up ^ Riffenburgh, R. H. (1999). Statistics in medicine. Boston: Academic Press. p. 196. ISBN 0-12-588560-1. 
  11. Jump up ^ Thompson B. Fallacies.
  12. Jump up ^ Logic via
  13. Jump up ^ Sicherer, Scott H. (1999). "Food allergy: When and how to perform oral food challenges". Pediatric Allergy & Immunology 10 (4): 226–234. doi:10.1034/j.1399-3038.1999.00040.x. 
  14. Jump up ^ Lee D (2005). Evaluating Medications and Supplement Products. via MedicineNet
  15. Jump up ^ Altman, D. G.; Bland, M. (1995). "Absence of evidence is not evidence of absence". British Medical Journal 311 (7003): 485. doi:10.1136/bmj.311.7003.485. 

Further reading[edit]

Philosophic burden of proof


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This article is about burden of proof as a philosophical concept. For other uses, see Burden of proof (disambiguation).
In epistemology, the burden of proof (Latin: onus probandi) is the obligation on a party in a dispute to provide sufficient warrant for their position.

Holder of the burden[edit]

When two parties are in a discussion and one asserts a claim that the other disputes, the one who asserts has a burden of proof to justify or substantiate that claim. [1] An argument from ignorance occurs when either a proposition is assumed to be true because it has not yet been proved false or a proposition is assumed to be false because it has not yet been proved true.[2][3] This has the effect of shifting the burden of proof to the person criticizing the proposition.[4]
While certain kinds of arguments, such as logical syllogisms, require mathematical or strictly logical proofs, the standard for evidence to meet the burden of proof is usually determined by context and community standards and conventions.[5][6]

In public discourse[edit]

Burden of proof is also an important concept in the public arena of ideas. Once participants in discourse establish common assumptions, the mechanism of burden of proof helps to ensure that all parties contribute productively, using relevant arguments.[7][8][9][10]

Proving a negative[edit]

A negative claim is a colloquialism for an affirmative claim that asserts the non-existence or exclusion of something. There are many proofs that substantiate negative claims in mathematics, science, and economics including Arrow's impossibility theorem.
A negative claim may or may not exist as a counterpoint to a previous claim. A proof of impossibility or an evidence of absence argument are typical methods to fulfill the burden of proof for a negative claim.[11][12]


Matt Dillahunty gives the example of a large jar full of gumballs to illustrate the burden of proof.[13][14] It is a fact of reality that the number of whole gumballs in the jar is either even or odd, but the degree of personal acceptance or rejection of claims about that characteristic may vary. We can choose to consider two claims about the situation, given as:
  1. The number of gumballs is even.
  2. The number of gumballs is odd.
These two claims can be considered independently, however, both claims represent the same proposition. Odd in this case means "not even" and could be described as a negative claim. Before we have any information about the number of gumballs, we have no means of checking either of the two claims. When we have no evidence to resolve the proposition, we may suspend judgment. From a cognitive sense, when no personal preference toward opposing claims exists, one may be either skeptical of both claims or ambivalent of both claims. [15][16][17] If there is a claim proposed and that claim is disputed, the burden of proof falls onto the proponent of the claim. If there is no agreeable evidence to support a claim, the claim is considered to be an argument from ignorance.

See also[edit]


  1. Jump up ^ Cargile, James (January 1997). "On the Burden of Proof". Philosophy (Cambridge University Press) 72 (279): 59–83. doi:10.1017/s0031819100056655. 
  2. Jump up ^ "Argumentum ad Ignorantiam". Philosophy 103: Introduction to Logic. Lander University. 2004. Archived from the original on 30 April 2009. Retrieved 2009-04-29. 
  3. Jump up ^ Dowden, Bradley. "Appeal to Ignorance". Internet Encyclopedia of Philosophy. 
  4. Jump up ^ Michalos, Alex (1969). Principles of Logic. Englewood Cliffs: Prentice-Hall. p. 370. usually one who makes an assertion must assume the responsibility of defending it. If this responsibility or burden of proof is shifted to a critic, the fallacy of appealing to ignorance is committed. 
  5. Jump up ^ Leite, Adam (2005). "A Localist Solution to the Regress of Justification". Australasian Journal of Philosophy 83 (3): 395–421 [p. 418]. doi:10.1080/00048400500191974. [t]he point of articulating reasons in defense of one’s belief is to establish that one is justified in believing as one does. 
  6. Jump up ^ Leite, Adam (2005). "A Localist Solution to the Regress of Justification". Australasian Journal of Philosophy 83 (3): 395–421 [p. 403]. doi:10.1080/00048400500191974. justificatory conversation...[is]...characterized by a person’s sincere attempt to vindicate his or her entitlement to a belief by providing adequate reasons in its defense and responding to objections. 
  7. Jump up ^ Goldman, Alvin (1994). "Argumentation and Social Epistemology". Journal of Philosophy 91 (1): 27–49. doi:10.2307/2940949. JSTOR 2940949. 
  8. Jump up ^ Eemeren, Frans van; Grootendorst, Rob (2004). A Systematic Theory of Argumentation. Cambridge: Cambridge University Press. p. 60. ISBN 0521830753. [t]here is no point in venturing to resolve a difference of opinion through an argumentative exchange of views if there is no mutual commitment to a common starting point. 
  9. Jump up ^ Brandom, Robert (1994). Making it Explicit. Cambridge: Harvard University Press. p. 222. ISBN 067454319X. [t]here are sentence types that would require a great deal of work for one to get into a position to challenge, such as 'Red is a color,' 'There have been black dogs,' 'Lighting frequently precedes thunder,' and similar commonplaces. These are treated as 'free moves' by members of our speech community—they are available to just about anyone any time to use as premises, to assert unchallenged. 
  10. Jump up ^ Adler, Jonathan (2002). Belief’s Own Ethics. Cambridge: MIT Press. pp. 164–167. ISBN 0262011921. 
  11. Jump up ^ Steven D. Hales (2005). "Thinking Tools: You Can Prove a Negative" (PDF). Bloomsburg University. 
  12. Jump up ^ T. Edward Dame (2009). Attacking Faulty Reasoning: A Practical Guide to Fallacy-Free Arguments. Cengage Learning. p. 17. ISBN 9780495095064. 
  13. Jump up ^ "The Atheist Experience". Episode 808. 7 April 2013. channelAustin 16.  Missing or empty |series= (help)
  14. Jump up ^ Matt Dillahunty (2013). Does God Exist? (Debate). Texas State University. 
  15. Jump up ^ "Metacognitive Model of Ambivalence: The Role of Multiple Beliefs and Metacognitions in Creating Attitude Ambivalence". 
  16. Jump up ^ "Reductionism, emergence, and burden of proof — part I". 
  17. Jump up ^ "Reductionism, emergence, and burden of proof — part II". 


Certainty is perfect knowledge that has total security from error, or the mental state of being without doubt.
Objectively defined, certainty is total continuity and validity of all foundational inquiry, to the highest degree of precision. Something is certain only if no skepticism can occur. Philosophy (at least, historical Cartesian philosophy) seeks this state.[citation needed]
It is widely held that certainty about the real world is a failed historical enterprise (that is, beyond deductive truths, tautology, etc.).[1] This is in large part due to the power of David Hume's problem of induction. Physicist Carlo Rovelli adds that certainty, in real life, is useless or often damaging (the idea is that "total security from error" is impossible in practice, and a complete "lack of doubt" is undesirable).[2]


Pyrrho – ancient Greece[edit]

Main article: Pyrrho
Pyrrho is credited as being the first Skeptic philosopher. The main principle of Pyrrho's thought is expressed by the word acatalepsia, which denotes the ability to withhold assent from doctrines regarding the truth of things in their own nature; against every statement its contradiction may be advanced with equal justification. Secondly, it is necessary in view of this fact to preserve an attitude of intellectual suspense, or, as Timon expressed it, no assertion can be known to be better than another.

Al-Ghazali – Islamic theologian[edit]

Main article: Al-Ghazali
Al-Ghazali was a professor of philosophy in the 11th century. His book titled The Incoherence of the Philosophers marks a major turn in Islamic epistemology, as Ghazali effectively discovered philosophical skepticism that would not be commonly seen in the West until Averroes, René Descartes, George Berkeley and David Hume. He described the necessity of proving the validity of reason—independently from reason. He attempted this and failed. The doubt that he introduced to his foundation of knowledge could not be reconciled using philosophy. Taking this very seriously, he resigned from his post at the university, and suffered serious psychosomatic illness. It was not until he became a religious sufi that he found a solution to his philosophical problems, which are based on Islamic religion; this encounter with skepticism led Ghazali to embrace a form of theological occasionalism, or the belief that all causal events and interactions are not the product of material conjunctions but rather the immediate and present will of God.

Ibn-Rushd - Averroes[edit]

Main article: Ibn Rushd
Latinized name Averroës
Averroes was a defender of Aristotelian philosophy against Ash'ari theologians led by Al-Ghazali. Averroes' philosophy was considered controversial in Muslim circles.[3] Averroes had a greater impact on Western European circles and he has been described as the "founding father of secular thought in Western Europe".

Descartes – 17th century[edit]

Descartes' Meditations on First Philosophy is a book in which Descartes first discards all belief in things which are not absolutely certain, and then tries to establish what can be known for sure. Although the phrase "Cogito, ergo sum" is often attributed to Descartes' Meditations on First Philosophy, it is actually put forward in his Discourse on Method. Due to the implications of inferring the conclusion within the predicate, however, he changed the argument to "I think, I exist"; this then became his first certainty.

Ludwig Wittgenstein – 20th century[edit]

On Certainty is a series of notes made by Ludwig Wittgenstein just prior to his death. The main theme of the work is that context plays a role in epistemology. Wittgenstein asserts an anti-foundationalist message throughout the work: that every claim can be doubted but certainty is possible in a framework. "The function [propositions] serve in language is to serve as a kind of framework within which empirical propositions can make sense".[4]

Degrees of certainty[edit]

Physicist Lawrence M. Krauss suggests that identifying degrees of certainty is under-appreciated in various domains, including policy making and the understanding of science. This is because different goals require different degrees of certainty—and politicians are not always aware of (or do not make it clear) how much certainty we are working with.[5]
Rudolf Carnap viewed certainty as a matter of degree (degrees of certainty) which could be objectively measured, with degree one being certainty. Bayesian analysis derives degrees of certainty which are interpreted as a measure of subjective psychological belief.
Alternatively, one might use the legal degrees of certainty. These standards of evidence ascend as follows: no credible evidence, some credible evidence, a preponderance of evidence, clear and convincing evidence, beyond reasonable doubt, and beyond any shadow of a doubt (i.e. undoubtable—recognized as an impossible standard to meet—which serves only to terminate the list).

Foundational crisis of mathematics[edit]

The foundational crisis of mathematics was the early 20th century's term for the search for proper foundations of mathematics.
After several schools of the philosophy of mathematics ran into difficulties one after the other in the 20th century, the assumption that mathematics had any foundation that could be stated within mathematics itself began to be heavily challenged.
One attempt after another to provide unassailable foundations for mathematics was found to suffer from various paradoxes (such as Russell's paradox) and to be inconsistent.
Various schools of thought on the right approach to the foundations of mathematics were fiercely opposing each other. The leading school was that of the formalist approach, of which David Hilbert was the foremost proponent, culminating in what is known as Hilbert's program, which sought to ground mathematics on a small basis of a formal system proved sound by metamathematical finitistic means. The main opponent was the intuitionist school, led by L.E.J. Brouwer, which resolutely discarded formalism as a meaningless game with symbols.[citation needed] The fight was acrimonious. In 1920 Hilbert succeeded in having Brouwer, whom he considered a threat to mathematics, removed from the editorial board of Mathematische Annalen, the leading mathematical journal of the time.
Gödel's incompleteness theorems, proved in 1931, showed that essential aspects of Hilbert's program could not be attained. In Gödel's first result he showed how to construct, for any sufficiently powerful and consistent finitely axiomatizable system—such as necessary to axiomatize the elementary theory of arithmetic—a statement that can be shown to be true, but that does not follow from the rules of the system. It thus became clear that the notion of mathematical truth can not be reduced to a purely formal system as envisaged in Hilbert's program. In a next result Gödel showed that such a system was not powerful enough for proving its own consistency, let alone that a simpler system could do the job. This dealt a final blow to the heart of Hilbert's program, the hope that consistency could be established by finitistic means (it was never made clear exactly what axioms were the "finitistic" ones, but whatever axiomatic system was being referred to, it was a weaker system than the system whose consistency it was supposed to prove). Meanwhile, the intuitionistic school had failed to attract adherents among working mathematicians, and floundered due to the difficulties of doing mathematics under the constraint of constructivism.
In a sense, the crisis has not been resolved, but faded away: most mathematicians either do not work from axiomatic systems, or if they do, do not doubt the consistency of Zermelo–Fraenkel set theory, generally their preferred axiomatic system. In most of mathematics as it is practiced, the various logical paradoxes never played a role anyway, and in those branches in which they do (such as logic and category theory), they may be avoided.


Doubt is not a pleasant condition, but certainty is absurd.
— Voltaire
In this world nothing can be said to be certain, except death and taxes.
There is no such thing as absolute certainty, but there is assurance sufficient for the purposes of human life.
If you tried to doubt everything you would not get as far as doubting anything. The game of doubting itself presupposes certainty.

See also[edit]


  1. Jump up ^ Peat, F. David (2002). From Certainty to Uncertainty: The Story of Science and Ideas in the Twentieth Century. National Academies Press. ISBN 978-0-309-09620-1. 
  2. Jump up ^
  3. Jump up ^ "Averroës (Ibn Rushd) > By Individual Philosopher > Philosophy". Retrieved 2012-10-13. 
  4. Jump up ^ Wittgenstein, Ludwig. "On Certainty". SparkNotes. 
  5. Jump up ^ "question center, SHAs – cognitive tools". 

External links[edit]