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Confusing correlation with causation, assuming causation because of correlation, or ignoring that there is some other factor that affects both of the things under discussion. Often summed up as "Correlation does not imply causation
- Magical Thinking
- Ignoring A Common Cause
- First one thing happens, then another thing happens. Therefore, the first thing caused the second thing. There must be a clear temporal connection between the two things.
- In an episode of NUMB3RS, Charlie tells Don about the ice cream-rape correlation. As the sales of ice cream goes up, so do the number of rapes. The key is both take place during summer.
- The West Wing had an episode named from the Latin name for this fallacy, "Post Hoc, Ergo Propter Hoc". In the episode, some of the White House staffers think President Bartlet's electoral problems with Texas stem from him making fun of their 'big hats'. Bartlet mentions the above stated phrase, correcting them that his problem with Texas is his immigration policy.
- Another staffer jokes that he lost Texas when he learned to speak Latin.
- This is more or less the entire premise of How I Met Your Mother. Seven seasons, we haven't met the mother, and more or less absolutely nothing of relevance has happened.
- Invoked by Sheldon in The Big Bang Theory when his mother claims that the prayers of her church group are responsible for his surviving in the Arctic.
- One Drabble comic demonstrates this. Ralph and another driver are stopped at a red light. The other guy is loudly complaining at the light as they wait for it to change, while Ralph counts down in his head. As Ralph finishes counting down, he suddenly pulls out his TV remote control, points it at the light, and presses a button... and the light turns green, much to the other guy's amazement. No, the remote didn't actually make the light change, Ralph just has this light's schedule memorized, knew when it would change, and felt like Mind Screwing somebody.
- One episode of Justice League features a journalist claiming that since white-collar crime has risen since the League formed, the League clearly causes that crime (in fact, given the League's style, it's entirely possible that the smarter criminals turn to white-collar rather than blue-collar crime to reduce the chances of Superman slapping them around Metropolis, but his logic still doesn't track).
- An even better example (from that same episode, that same scene, and that same character) would be when the talk show host demands that the Flash explain the fact that since the League was formed 50% of all marriages end in divorce, and the rest end in death. Not only is there no connection between the founding of the Justice League and divorce rates, of course all the other marriages end in death. The couples who didn't get divorced simply grew old and died naturally. Hence the phrase "till death do you part".
- In one episode of South Park, banning Kentucky Fried Chicken causes a violent black market economy to spring up. Meanwhile, legalizing medical marijuana causes people to deliberately give themselves testicular cancer so they can legally get marijuana. The authorities look at the situation, and deduce that medical marijuana causes gang violence and Kentucky Fried Chicken prevents testicular cancer.
- Another prominent example often used in statistics classes: The declining number of storks is responsible for the declining birth rate. In truth, the stork population and the birth rate of humans are usually both being affected by some third factor.
- "Before women got the vote, there were no nuclear weapons!" is sometimes offered as an example of this kind of logical error - while in all probability this idea has never been advanced as a serious argument, it does throw a stark illumination on political screeds from either end of the spectrum. (Also, it's factually incorrect even when constrained to "Enlightened Western Democracies", since Switzerland only granted universal suffrage in 1975, some thirty years after the first use of the atom bomb.)
- The "gateway drug" theory relies heavily on this fallacy. Typically, it is noted that out of a sample of heavy drug users, over 95% of them started out using marijuana (or alcohol). The same claim could be made about bread or water. A less fallacious case for marijuana as a gateway drug would be citing the percentage of marijuana smokers who progress to harder drugs. That number is nowhere near as impressively high, though.
- This is also subject to the "Ignoring the Common Cause" variant, as showing people progressing from weed to hard drugs doesn't prove that the weed caused the escalation. Another likely explanation is that the same factor (poor judgment or impulse control, risk-seeking personalities) led to the person taking both drugs, but that they started with weed because it was cheaper or easier to obtain.
- It is also suggested that when the people first hear horror stories about marijuana, and after experimenting realize that its effects are far less impressive and dangerous than advertised, think that the same must apply to all the other drugs, as well.
- Want to drive a Psychology major insane? Tell him Prozac can cause suicide. After he stops frothing at the mouth, he'll try to explain: "Prozac is prescribed to people with Depression. Prozac, like all Depression Medication, takes at least a few weeks to start working. Some depressed teenager, but no higher than normal, killed themselves after starting it, but before it started working. No one explained this to their soccer moms or, apparently, to you!"
- Fluoxetine is widely regarded by the American Medical Association as increasing the risk of suicidal ideation but not causing suicide. It actually carries a "Black Box Warning" saying there is an increased chance of suicidal ideation with the use of many anti-depressants in patients under 25. Older adults showed decreased suicidal idealization. The "folk" explanation in the medical community is some depressed individuals are "too depressed to kill themselves," and when they feel better, they start thinking about steps to "end their depression." For most people, that means positive changes. For others...more drastic solutions come to mind. And the anorgasmia can't help.
- When a laptop processor overheats, the cooling fan spins faster to try and compensate, a normal responses coded in the system BIOS. When this happens, a large number of people will call in technical support insisting for a new fan because it's "clearly heating up the system by spinning too hard."
- Magical Thinking
- Ignoring A Common Cause
- A less well-known but equally commonly used sibling fallacy to Post hoc, Cum hoc is saying that because A and B occur together, A causes B. The difference between Post hoc and Cum hoc is that Post hoc has a clear temporal relationship—A happens first, then B, while Cum hoc does not have that temporal relationship; the two things may occur at the same time. Many examples that are called Post hoc are really Cum hoc. Like Post Hoc, Cum Hoc ignores the possibility that there may be one or more additional factors that affect both A and B, or even that B may be in fact causing A.
- This is a common fallacy when one compares two graphs to each other. One classic example used by racists is to use crime rate figures sorted by race to "prove" that immigrants are predisposed towards becoming criminals; this ignores that immigrants are statistically more likely to live in poverty, and people who live in poverty, regardless of race, are more likely to turn to crime.
- Journalism is particularly prone to committing this fallacy, since journalists are obliged to turn a complex issue into a snappy headline. So, for example, a study showing a correlation between living near high-tension power-lines and certain types of cancer will be covered as "researchers prove power lines linked to cancer."
- In The Simpsons episode "Much Apu About Nothing", an isolated bear attack leads the mayor to fund a massive Bear Patrol scheme. Homer claims that the lack of bears proves the Bear Patrol works, at which point Lisa points out that you might as well say that a rock keeps tigers away, since she's holding the rock, and she can't see any tigers. Homer's response? "Lisa, I want to buy your rock."
- This comic from PHD Comics makes fun of journalists' tendency to use this fallacy when reporting on scientific findings.
- As noted in Darrel Huff's famous book, How To Lie With Statistics, a bunch of islanders once noticed that whenever they were sick, they didn't have lice, whereas whenever they were healthy, they did. Their conclusion? Having lice makes you healthy; everyone should have them. Thus they managed to draw a conclusion completely opposed to the reality, which was that having lice was making them sick, which gave them a fever, and that fever was subsequently driving away the lice.
- This fallacy often comes up in discussions of violence related to video games. The claim is that violent video games cause or encourage violent behavior in real life. The other possible sources of correlation include, but are not limited to; that violence-prone people tend to enjoy violent games; that some violent people prefer non-social activities that include games; that video games are simply becoming ubiquitous enough that almost every child plays them, so naturally the violent ones did too.
- Many firearm-related campaigns have their roots in this sort of thinking. For example, the scare regarding Teflon-coated "cop killer" bullets. Armor-piercing bullets are generally made of harder material than standard ammunition (such as solid brass), so use a Teflon coating to reduce barrel wear. The scare falsely identified the Teflon coating as the reason the bullets could pierce armor, resulting in several states banning ammunition with such a coating despite that armor-piercing ammunition was already banned at the Federal level. The Assault Weapons Ban is a similar case, where superficial aspects of a weapon with no bearing on performance (for example, if it had a lug for fitting a bayonet) were used to judge if it was an "assault weapon", as opposed to what the weapon's mechanism was actually capable of.
- This fallacy was used by Frederic Wertham to establish the Comics Code. He noted that juvenile delinquents tended to read comic books, so comic books must cause juvenile delinquency. Of course, during this time period comic books were more popular in America than ever before or ever since - the typical child read about 5 comics a week. Even adults weren't far behind, many of whom had picked up the habit during WWII when comics were sent overseas to servicemen.
- This has also been used to argue that listening to country music causes higher suicide rates, since places with a higher percentage of country music listening tend to also have a higher percentage of suicide. Of course, the places that listen to country music tend to be poor and rural—and poor, rural areas tend to have relatively high rates of suicide.
- A similar argument is that slow country songs lead to alcoholism. This began when someone noticed that alcohol consumption in bars increased when bands played slow songs. Did it occur to this genius that people simply stopped dancing and ordered more drinks at that time?
- Pastafarianism claims that pirates prevent global warming, as the number of pirates is decreasing while temperatures increase, as a parody of this type of thinking to demonstrate the flaw in logic.
- A particularly absurd example: The pretty-much-undefinable Column 8 in the Sydney Morning Herald once featured a letter correlating the difficulty of the newspaper's Sudoku with the price of petrol.
- Autism and Thimerisol. Oh, where to begin. When doctors started to include Thimerisol in vaccines, in the early 1990s, the rates of autism increased as well (really due to autism becoming more well known and thus diagnosed more), and despite several studies finding no link between Thimerisol and autism (and removal of Thimerisol from vaccines), people still insist that the Thimerisol in vaccines causes autism.
- Something similar happens with MMR, with children showing symptoms of autism shortly after receiving the first dose. Never mind that MMR vaccinations are typically first administered in 1-year-old children, i.e. a few months before the age where autism starts, y'know, showing symptoms.
- Philosophy teachers often use the example of how ice cream causes rapes as an example of the fallacy. The number of rapes always increases along with the consumption of ice cream. Of course, the real reason behind this is that the two unrelated activities correlate in similar manner with the weather.
- Any time a claim is made that reads, "I took this remedy, and now I feel better, so it works." Whether the remedy is traditional evidence based medicine, traditional herbal remedies, or New Age alternative health based, this claim is fallacious. The best way to determine effectiveness of a remedy is through a double-blind clinical trial.
- The same is true of claims of divine intervention or prayer. A claim that prayer or God's will saved an individual runs afoul of this fallacy. Whether the claim is true or not is not a good thing to argue here. However, the claim, "I had cancer. I saw a faith healer. My cancer spontaneously went into remission. Therefore prayer worked," is logically fallacious.
- This last has an interesting connection to Catholicism. In order to be canonized—recognized as a saint—a dead person must be provably in Heaven. Now, in Catholic doctrine, lots of people are saints in that they are in Heaven, but not canonized because the Church on Earth can't know for sure. So they have to produce evidence that the deceased is there and not Purgatory, and the main way to do this is to look for miracles. The most common kind of claimed miracles are the medical sort—you get sick, you pray for the saint's intercession, you get better against the odds. However, to avoid this fallacy as much as possible, the Church rigorously investigates the claimed miracle to see if it has any conceivable rational explanation; if the doctors can gin up any theory, however implausible, that explains your cure, the claimed miracle is insufficient grounds for canonization. Only if the doctors are completely stumped and have no idea how you could be cured is it considered to be a likely miracle, and frankly at that point, the miraculous explanation becomes more believable if you're a believer in the first place. To its credit, the Church recognizes that it might very well be wrong and be executing the fallacy anyway, but it certainly minimizes the chances.
- A favorite tactic of journalists trying to make attention-grabbing articles and people trying to promote a specific lifestyle is to claim "people who do X are healthier/live longer/etc., therefore you should do X because it is good for you." Usually, it is much more likely that healthy and/or health-conscious people are more likely to do X, or that people have to be healthy in order to do X on a regular basis. For examples:
- Of the first type: The healthiest people tend to be people who floss. This is not to say that flossing causes you to be the healthiest kind of person, but rather, those who floss tend to do every other generally recommended healthy action, with flossing being one of the most rare.
- Of the second type: People who get up in the morning and run a mile before breakfast tend to be some of the healthiest people around. Sure, exercise helps you be healthy, but when's the last time you saw an out-of-shape guy who was physically capable of running a mile?