Selection bias

Cogito ergo sum
Logic and rhetoric

Key articles

* Logical fallacy
* Syllogism
* Argument

General logic

* Argument from authority
* Hoyle's fallacy
* Bait-and-switch
* Shoehorning
* Apophasis
* If-by-whiskey

Bad logic

* Confounding factor
* Flying carpet fallacy
* Rapoport's Rules
* Bullshit
* Logical fallacy
* دوگانگی مرتن

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“”I don't understand all the negativity around Russian roulette. Everyone I ever talked to who's played it is doing fine.

—u/robdingo36

Selection bias is the bias that occurs in a survey or experimental data when the selection of data points isn't sufficiently random to draw a general conclusion. If selection bias isn't accounted for or acknowledged, and the results are claimed to be widely applicable, it is known as the spotlight fallacy.

## Contents

* 1 Examples
* 1.1 In science
* 1.2 In the anti-gender movement
* 2 See also
* 2.1 Want to read this in another language?
* 3 References

## Examples[edit]

Examples of selection bias are rife amongst online polls. These polls are completed only by visitors to the site, and so those with an interest in the website's mission or ones that agree with its POV are the only ones to be surveyed. While the informality of online polls is often clear and admitted to, it's important to not draw generalised conclusions from them.

A website devoted to preventing harassment of women unsurprisingly concluded that nearly all women were victims of harassment at some point;[1] meanwhile, a poll on alternative medicine managed to receive more votes than people who read the associated article, a sure sign that something very odd was happening.[2] Polls by the right-wing news site WND are as famous for showing that their readership have right-wing views as for having ridiculous numbers of available options.[3] Similarly, Facebook's recent "Questions" feature spreads via friends in similar circles who are likely to be in a similar area – so asking "what town is the best?" will be easily slanted. Reviews, of restaurants, films, or medical services for example, may also be highly biased towards the negative because people are more likely to rant on the internet after having a bad time, than they are to rave about something after a good or adequate time.

### In science[edit]

Scientific selection bias is a massive problem and often great pains are taken to avoid it. In Andrew Wakefield's heavily discredited paper on the MMR vaccine, he took 12 children who had behavioural disorders and attempted to link them to vaccines. No attempt was made, in the paper, to look at children without behavioural disorders to see if their exposure to the MMR vaccine was greater or less. This would also be an example of confirmation bias.

Selection bias doesn't just apply to people. With meta-analyses of existing research and scientific literature, the cited literature may be subjected to a selection bias based on several factors. Only certain types of studies might be included or only ones indexed in certain journals – certainly meta-analysis is restricted to data that is published, and publication bias is a huge problem in itself. This is why good meta-analyses clearly state their search terms and criteria and include all papers that fit these terms, so selection bias is either minimised or at least acknowledged and controlled objectively. Often in pseudoscience, the literature is chosen specifically to support a point of view. In this case, it is referred to as cherry picking.

Time scale is also a possible biasing factor. Surveys done only at certain times or for too short a period of time will bias a result so that it is not applicable to other times. This is often seen in political approval ratings, where approval during a specific time frame (such as during a crisis or scandal) is not representative of public approval over the course of several years. A clear bias can be made if sample data is restricted to a certain time frame that emphasizes a change. RationalWiki's pageviews between March 15th and March 21st 2011 went down significantly according to Alexa.com,[4] but this isn't representative of a longer trend that actually shows an increase. Again, intentional massaging of data by cutting off certain time periods is cherry picking, and greatly frowned up on science and statistics, but is often the way global warming denialism presents data.

### In the anti-gender movement[edit]

See the main article on this topic: Gender ideology

Another example of selection bias is in several research articles conducted by anti-trans activists, notably TERFs. One notable example of this is the Littman 2018 ROGD study, conducted using a sample of parents frequenting websites which are biased against gender affirmation of trans youth (without even surveying the trans youth themselves). Another example is an article published by the BBC in 2021 with a conclusion that FtM transition is a form of conversion therapy and MtF transition is a means to prey on cis lesbians; however, in this case, only lesbians which are in a transphobic organization were surveyed for the research, creating an innate bias.

## See also[edit]

* Cherry picking
* Confirmation bias
* Dewey Defeats Truman, an example of how bad polling prompted a newspaper to call an election prematurely for the losing candidate
* Spotlight fallacy
* Push poll
* Survivorship bias - a form of selection bias focusing on what has survived to the present and ignoring what must have been lost.

###

Want to read this in another language?

Se você procura pelo artigo em Português, ver Viés de seleção.

## References[edit]

1. ↑ Stop Street Harassment - Statistics
2. ↑ Vote on alternative medicine falls victim to dark arts of the internet
3. ↑ WND - Why do you think CBS News ratings are so low? As a random example.
4. ↑ Alexa.com - Rationalwiki.org, site info \- Observing the noise, it's possible to clip the data at several points to show many different trends.

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Articles about logical fallacies

Informal fallacies: |

Appeal to tradition • Appeal to novelty • Appeal to nature • Argument from morality • Argumentum ad martyrdom • Big words • Certum est quia impossibile est • Morton's fork • Friend argument • Exception that proves the rule • Extended analogy • Hindsight bias • Race card • Moralistic fallacy • Release the data • Gish Gallop • Terrorism-baiting • Uncertainty tactic • Greece-baiting • Ham Hightail • Red-baiting • Gore's Law • Nazi analogies • Mistaking the map for the territory • Red herring • Quidquid latine dictum sit, altum videtur • Presentism • Sunk cost • Two wrongs make a right • Flying carpet fallacy • My enemy's enemy • Appeal to ancient wisdom • Danth's Law • Argumentum ad lunam • Balance fallacy • Golden hammer • Loaded question • Escape to the future • Word magic • Spider-Man fallacy • Sanctioning the devil • Appeal to mystery • Informal fallacy • Common sense • Post-designation • Hyperbole • Relativist fallacy • Due diligence • Straw man • Good old days • Appeal to probability • Infinite regress • Circular reasoning • Media was wrong before • Is–ought problem • Ad iram • Just asking questions • Pink-baiting • Appeal to faith • Appeal to fear • Appeal to bias • Appeal to confidence • Appeal to consequences • Appeal to emotion • Appeal to flattery • Appeal to gravity • Appeal to hate • Argument from omniscience • Argument from silence • Argumentum ad baculum • Argumentum ad fastidium • Association fallacy • Broken window fallacy • Category mistake • Confounding factor • Counterfactual fallacy • Courtier's Reply • Damning with faint praise • Definitional fallacies • Equivocation • Fallacy of accent • Fallacy of accident • Fallacy of amphiboly • Gambler's fallacy • Imprecision fallacy • Moving the goalposts • Nirvana fallacy • Overprecision • Pathos gambit • Pragmatic fallacy • Quote mining • Argumentum ad sarcina inserta • Science doesn't know everything • Slothful induction • Spotlight fallacy • Style over substance • Toupee fallacy • Genuine but insignificant cause • Argument from incredulity • Appeal to age • Argumentum ad nauseam • Phantom distinction • Appeal to common sense • Argumentum ad hysteria • Omnipotence paradox • Argument from etymology • Appeal to trauma • Countless counterfeits fallacy •

| Ad hoc: |

No True Scotsman • Moving the goalposts • Escape hatch • Handwave • Special pleading • Slothful induction • Nirvana fallacy • God of the gaps • PIDOOMA • Ad hoc • Tone argument •

| Arguments from ignorance: |

Science doesn't know everything • Argument from incredulity • Argument from silence • Toupee fallacy • Appeal to censorship • Science was wrong before • Holmesian fallacy • Argument from omniscience • Willful ignorance • Argument from ignorance •

| Causation fallacies: |

Post hoc, ergo propter hoc • Correlation does not imply causation • Wrong direction • Counterfactual fallacy • Regression fallacy • Gambler's fallacy • Denying the antecedent • Genuine but insignificant cause •

| Circular reasoning: |

Infinite regress • Argument by assertion • Argumentum ad dictionarium • Appeal to faith • Circular reasoning • Self-refuting idea •

| Emotional appeals: |

Appeal to fear • Appeal to emotion • Appeal to confidence • Deepity • Argumentum ad baculum • Appeal to shame • Appeal to flattery • Tone argument • Appeal to money • Argumentum ad fastidium • Appeal to gravity • Appeal to consequences • Loaded language • Style over substance • Appeal to pity • Appeal to hate • Pathos gambit • Shaming • Degenerate • Abomination •

| Fallacies of ambiguity: |

Fallacy of accent • Equivocation • Fallacy of amphiboly • Quote mining • Fallacy of ambiguity • Moral equivalence • Scope fallacy • Suppressed correlative • Not as bad as • Etymology • Continuum fallacy • Wronger than wrong • Definitional fallacies • Code word • Phantom distinction •

Formal fallacies: |

Confusion of the inverse • Denying the antecedent • Non sequitur • Affirmative conclusion from a negative premise • Not even wrong • Chewbacca Defense • Affirming a disjunct • Illicit process • Four-term fallacy • Negative conclusion from affirmative premises • Fallacy fallacy • Substituting explanation for premise • Enthymeme • Syllogism • Formal fallacy • Existential assumption • Masked man fallacy • Self-refuting idea • Argument by gibberish • One single proof • Affirming the consequent • False dilemma • Conjunction fallacy •

Fallacious arguments: |

Bumblebee argument • Fatwa envy • Gotcha argument • Hoyle's fallacy • Intuition pump • Logic and Creation • Not Circular Reasoning • Peanut butter argument • Great Beethoven fallacy • Fallacy of unique founding conditions • Evil is the absence of God • Argument from first cause • How do you know? Were you there? • Argument from design • Argument from beauty • Appeal to nature • Solferino fallacy • Religious scientists • Nothing to hide • Argument from fine tuning • Creep shaming • "I used to be an atheist" • Atheism as a religion • Argumentum ad populum • Argument from morality • Anti-environmentalism • Appeal to bias • Apophasis • Argumentum ad nauseam • Appeal to censorship • Argumentum ad sarcina inserta • Blaming the victim • Bait-and-switch • Danth's Law • Chewbacca Defense • Canard • DARVO • Demonization • Escape hatch • Friend argument • Everyone is racist • Gish Gallop • Greece-baiting • Gore's Law • Ham Hightail • Just asking questions • Leading question • Loaded language • Linking to authority • Loaded question • Lying by omission • Motte and bailey • Nazi analogies • Moving the goalposts • One single proof • Pink-baiting • One-way hash argument • Pathos gambit • Quote mining • Poisoning the well • Quidquid latine dictum sit, altum videtur • Race card • Red-baiting • Red herring • Release the data • Science was wrong before • Shill gambit • Straw man • Silent Majority • Uncertainty tactic • Style over substance • Terrorism-baiting • Weasel word • What's the harm (logical fallacy) • Whataboutism • Bullshit • Logical fallacy • Banana argument • Scapegoat • How come there are still monkeys? • Anti-racist is a code word for anti-white • Ontological argument • Omnipotence paradox • Presuppositionalism • Just a joke • Countless counterfeits fallacy •

Conditional fallacies: |

Slippery slope • What's the harm (logical fallacy) • Special pleading • Conditional fallacy • On the spot fallacy • Appeal to the minority • Argumentum ad populum • Galileo gambit • Professor of nothing •

| Genetic fallacies: |

Genetic fallacy •

|  | Appeals to authority: |

Ipse dixit • Appeal to confidence • Argumentum ad populum • Argument from authority • Linking to authority • Silent Majority • Invincible authority • Appeal to celebrity • Ultracrepidarianism • Appeal to the minority • Galileo gambit • Appeal to identity • Weasel word • Professor of nothing • Euthyphro dilemma • Divine command theory •

|  | Ad hominem: |

Ad iram • Argumentum ad cellarium • Bulverism • Poisoning the well • Blaming the victim • Tu quoque • Whataboutism • Nutpicking • Jonanism • Demonization • Shill gambit • Appeal to bias • Fallacy of opposition • Association fallacy • Damning with faint praise • Pathos gambit • Appeal to identity • Argumentum ad hominem • Nazi analogies • Not an argument • Nothing to hide • Scapegoat • 地下室论证 •

| Imprecision fallacies: |

Apex fallacy • Overprecision • Cherry picking • Overgeneralization • Texas sharpshooter fallacy • False analogy • Appeal to fiction • Spotlight fallacy • Pragmatic fallacy • Anecdotal evidence • Category mistake • Nutpicking • Imprecision fallacy • Confounding factor • Fallacy of accident • Neyman's bias •

Valid logical methods: |

Rapoport's Rules • Negative evidence • Reductio ad absurdum •

Fallacy collections: |

SeekFind • Nizkor Project • Fallacy Files • Your Logical Fallacy Is • Logically Fallacious •

Articles on Cognitive biases

Outcome bias - Confirmation bias - Clustering illusion - Demonization - Hindsight bias - Confabulation - Framing - Just world fallacy - Overconfidence effect - Walled garden - Survivorship bias - Frequency illusion - Overgeneralization - Response bias - Experimenter bias - Dunning–Kruger effect - Moral licensing - Ultimate attribution error - Gambler's fallacy - Delusion - Viés de seleção - Conjunction fallacy - Outgroup