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Encyclopedia > False positive

A false positive, also called a Type I error, exists when a test incorrectly reports that it has found a positive result where none really exists.

Detection algorithms of all kinds often create false positives. For example, optical character recognition (OCR) software may detect an 'a' where there are only some dots that look like an a to the algorithm being used. Flowcharts are often used to represent algorithms. ... Optical character recognition, usually abbreviated to OCR, involves computer software designed to translate images of typewritten text (usually captured by a scanner) into machine-editable text, or to translate pictures of characters into a standard encoding scheme representing them in (ASCII or Unicode). ...

The false positive rate is the proportion of negative instances that were erroneously reported as positive. It is equal to 1 minus the specificity of the test. In binary testing, e. ...

${rm false positive rate} = frac{rm number of false positives}{rm number of negatives}$

In statistical hypothesis testing, this fraction is sometimes described as the size of the test, and is given the symbol α. One may be faced with the problem of making a definite decision with respect to an uncertain hypothesis which is known only through its observable consequences. ... Alpha (uppercase Î‘, lowercase Î±) is the first letter of the Greek alphabet. ...

## False positives vs. false negatives

When developing detection algorithms (that is, tests) there is a tradeoff between false positives, and false negatives (in which an actual match is not detected). A threshold value can be varied to make the algorithm more restrictive or more sensitive. Restrictive algorithms risk rejecting true positives while more sensitive algorithms risk accepting false positives. A false negative, also called a miss, exists when a test reports, incorrectly, that a signal was not detected when, in fact, was present. ... Look up Threshold on Wiktionary, the free dictionary In general, a threshold is a fixed location or value where an abrupt change is observed. ...

## False positives in medicine

False positives are a significant issue in medical testing. In some cases, there are two or more tests that can be used, one of which is simpler and less expensive, but less accurate, than the other. For example, the simplest tests for HIV and hepatitis in blood have a significant rate of false positives. These tests are used to screen out possible blood donors, but more expensive and more precise tests are used in medical practice, to determine whether a person is actually infected with these viruses. Medicine is the branch of health science and the sector of public life concerned with maintaining human health or restoring it through the treatment of disease and injury. ... Human immunodeficiency virus, commonly known by the initialism HIV (formally known as HTLV-III and lymphadenopathy-associated virus), is a retrovirus that primarily infects vital components of the human immune system such as CD4+ T cells, macrophages and dendritic cells. ... Hepatitis is a gastroenterological disease, featuring inflammation of the liver. ... Blood transfusion is the taking of blood or blood-based products from one individual and inserting them into the circulatory system of another. ...

Perhaps the most widely discussed false positives in medicine come from screening mammography, a test to detect breast cancer. The US rate of false positive mammograms is up to 15%, the highest in world. The lowest rate in the world is in Holland, 1%. The lowest rates are generally in Northern Europe where mammography films are read twice and a high threshold for additional testing is set. One consequence of the US’s high false positive rate is that, in a ten year period, half of American women receive a false positive mammogram. False positive mammograms are costly, with over \$100 million spent annually in the US on unnecessary follow-up testing and treatment. They also cause women unneeded anxiety. Mammography of the right breast Mammography is the process of using low-dose X-rays (usually around 0. ...

False positives are also problematic in biometric scans, such as retina scans or facial recognition, when the scanner incorrectly identifies someone as matching a known person, either a person who is entitled to enter the system, or a suspected criminal. At Disney World, biometric measurements are taken of the fingers of multi-day pass users to ensure that the pass is used by the same person from day to day. ... Italic text Human eye cross-sectional view. ... A facial recognition system is a computer-driven application for automatically identifying a person from a digital image. ...

False positives can produce serious and counterintuitive problems when the condition being searched for is rare. If a test has a false positive rate of one in ten thousand, but only one in a million samples (or people) is a true positive, most of the "positives" detected by the test will be false. The probability that an observed positive result is a false positive may be calculated, and the problem of false positives demonstrated, using Bayes' theorem. Bayes theorem is a result in probability theory, which relates the conditional and marginal probability distributions of random variables. ...

## Security Screening

False positives are routinely found every day in security screening in airports. The security alarms are intended to prevent weapons being brought onto aircraft, yet they are set to such high sensitivity that they alarm many times a day for minor items such as keys, belt buckles, mobile phones. The ratio of False Positives to True Positives (detecting a would-be terrorist) is thus very high. Almost every alarm is a False Positive, hence the Positive Predictive Value of these tests is very low. See: Sensitivity (electronics) Sensitivity (human) Sensitivity (tests) For sensitivity in finance, see beta coefficient This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ...

## False positives in computer database searching

In computer database searching, false positives are documents that are retrieved by a search despite their irrelevance to the search question. False positives are common in full text searching, in which the search algorithm examines all of the text in all of the stored documents in an attempt to match one or more search terms supplied by the user. In computer science, particularly searching, relevance is a score assigned to a search result, representing how well the result meets the information need of the user who issued the search query. ... Full text search is a technique for searching a computer-stored text document based on its entire contents. ... In computer science, a search algorithm, broadly speaking, is an algorithm that takes a problem as input and returns a solution to the problem, usually after evaluating a number of possible solutions. ...

Most false positives can be attributed to the deficiencies of natural language, which is often ambiguous: the term "home," for example, may mean "a person's dwelling" or "the main or top-level page in a Web site." The false positive rate can be reduced by using a controlled vocabulary, but this solution is expensive because the vocabulary must be developed by an expert and applied to documents by trained indexers. The term natural language is used to distinguish languages spoken and signed (by hand signals and facial expressions) by humans for general-purpose communication from constructs such as writing, computer-programming languages or the languages used in the study of formal logic, especially mathematical logic. ... A controlled vocabulary (also called a taxonomy) is a carefully selected list of words and phrases, which are used to tag units of information so that they may be more easily retrieved by a search. ...

## False positives and spam

The term "False positive" is also used when spam filtering or spam blocking techniques wrongly classify a legitimate email message as spam and as a result interferes with its delivery. A mail filter is a piece of software which takes an input of an email message. ... A typical spam advertisement Email spam is a subset of spam that involves sending nearly identical messages to thousands (or millions) of recipients. ...

The opposite, a False Negative, occurs when filtering allows a spam email to be delivered to a user's inbox.

While most anti-spam tactics can block or filter a high percentage of unwanted emails, doing so without creating significant false-positive results is a much more demanding task.

A commonly referenced sub-category is the "Critical False-Positive." This term is used to distinguish the accidental blocking of mass-emails that may not be spam, but are not generally regarded as critical communications, in contrast with user to user messages and automated transaction notifications where timely delivery is much more important.

## False positives and malware

The term False positive is also used when antivirus software wrongly classifies a file as a virus. The incorrect detection may occur either by heuristics or by an incorrect virus signature in a database. Similar problems can occur with antitrojan or antispyware software. Malware (a portmanteau of malicious software) is software designed to infiltrate or damage a computer system, without the owners consent. ... Anti-virus software consists of computer programs that attempt to identify, thwart and eliminate computer viruses and other malicious software (malware). ... The human immunodeficiency virus (HIV) A virus is a submicroscopic parasite that infects cells in biological organisms. ... For heuristics in computer science, see heuristic (computer science) Heuristic is the art and science of discovery and invention. ... Anti-Trojan software is a specialized piece of software used to detect a Trojan horse. ... Strictly defined, spyware consists of computer software that gathers and reports information about a computer user without the users knowledge or consent. ...

## False positives and ghost investigation

False positive has been adopted by paranormal or ghost investigation groups to describe a photograph, recording, or other evidence that incorrectly appears to have a paranormal origin. In other words, a false positive in this context is a disproven piece of media (image, movie, audio recording, etc.) that has a normal explanation. Several sites provide examples of false positives, including The Atlantic Paranormal Society (TAPS) and Moorestown Ghost Research. A ghost is an alleged non-corporeal manifestation of a dead person (or, rarely, an animal). ... Anomalous phenomena are phenomena which are observed and for which there are no suitable explanations in the context of a specific body of scientific knowledge, e. ... A ghost is an alleged non-corporeal manifestation of a dead person (or, rarely, an animal). ...

Results from FactBites:

 HIV & AIDS - False Positive Viral Loads (6966 words) Although it is reasonable that false positive viral loads would appear any time there is a great deal of cell death because of the high quantities of RNA that are released when cells die in large numbers, no controlled studies were found that attempt to determine what factors influence the likelihood of false positive results. In contrast to the high rate of false positive results observed with gag primers, env DNA [env is another protein thought to be specific to HIV] was not detected by laboratory B in any of the specimens from either seronegative or seropositive individuals. False positive viral loads occur commonly in 3 to 10% of people who are HIV negative, with the highest reported rate being 60%.
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