What are common types of fallacy in research?

A fallacy is a mistaken belief, particularly one based on unsound arguments or one that lacks the evidence to support it. Common types of fallacy that may compromise the quality of your research are:

Correlation/causation fallacy: Claiming that two events that occur together have a cause-and-effect relationship even though this can’t be proven
Ecological fallacy: Making inferences about the nature of individuals based on aggregate data for the group
The sunk cost fallacy: Following through on a project or decision because we have already invested time, effort, or money into it, even if the current costs outweigh the benefits
The base-rate fallacy: Ignoring base-rate or statistically significant information, such as sample size or the relative frequency of an event, in favor of less relevant information e.g., pertaining to a single case, or a small number of cases
The planning fallacy: Underestimating the time needed to complete a future task, even when we know that similar tasks in the past have taken longer than planned

Frequently asked questions: Fallacies

Is no true Scotsman always a fallacy?: “No true Scotsman” arguments aren’t always fallacious. When there is a generally accepted definition of who or what constitutes a group, it’s reasonable to use statements in the form of “no true Scotsman.”

For example, the statement that “no true pacifist would volunteer for military service” is not fallacious, since a pacifist is, by definition, someone who opposes war or violence as a means of settling disputes.
How to avoid base rate fallacy?: Base rate fallacy can be avoided by following these steps:

Avoid making an important decision in haste. When we are under pressure, we are more likely to resort to cognitive shortcuts like the availability heuristic and the representativeness heuristic. Due to this, we are more likely to factor in only current and vivid information, and ignore the actual probability of something happening (i.e., base rate).

Take a long-term view on the decision or question at hand. Look for relevant statistical data, which can reveal long-term trends and give you the full picture.

Talk to experts like professionals. They are more aware of probabilities related to specific decisions.
Why is equivocation a fallacy?: Equivocation is a fallacy because it is a form of argumentation that is both misleading and logically unsound. When the meaning of a word or phrase shifts in the course of an argument, it causes confusion and also implies that the conclusion (which may be true) does not follow from the premise.

The equivocation fallacy is an informal logical fallacy, meaning that the error lies in the content of the argument instead of the structure.
What is an equivocation fallacy example in advertising?: In advertising, the equivocation fallacy is often used to create a pun. For example, a billboard company might advertise their billboards using a line like: “Looking for a sign? This is it!” The word sign has a literal meaning as billboard and a figurative one as a sign from God, the universe, etc.
Why are fallacies misleading?: Fallacies are arguments that contain some type of reasoning error. Regardless of whether they are used intentionally or by error, they weaken an argument by using erroneous beliefs, illogical arguments, or deception.

As a result, they shift the focus of a discussion to unrelated topics or side issues and can thus be misleading. For example, the genetic fallacy shifts the attention to the source or origin of an argument instead of presenting evidence to refute the argument itself.
What are fallacies of relevance?: Fallacies of relevance are a group of fallacies that occur in arguments when the premises are logically irrelevant to the conclusion. Although at first there seems to be a connection between the premise and the conclusion, in reality fallacies of relevance use unrelated forms of appeal.

For example, the genetic fallacy makes an appeal to the source or origin of the claim in an attempt to assert or refute something.
What is the difference between the ad hominem fallacy and the genetic fallacy?: The ad hominem fallacy and the genetic fallacy are closely related in that they are both fallacies of relevance. In other words, they both involve arguments that use evidence or examples that are not logically related to the argument at hand. However, there is a difference between the two:

In the ad hominem fallacy, the goal is to discredit the argument by discrediting the person currently making the argument.

In the genetic fallacy, the goal is to discredit the argument by discrediting the history or origin (i.e., genesis) of an argument.
What is another name for false dilemma fallacy?: False dilemma fallacy is also known as false dichotomy, false binary, and “either-or” fallacy. It is the fallacy of presenting only two choices, outcomes, or sides to an argument as the only possibilities, when more are available.
How do I avoid false dilemma fallacy?: The best way to avoid a false dilemma fallacy is to pause and reflect on two points:

Are the options presented truly the only ones available? It could be that another option has been deliberately omitted.

Are the options mentioned mutually exclusive? Perhaps all of the available options can be selected (or be true) at the same time, which shows that they aren’t mutually exclusive. Proving this is called “escaping between the horns of the dilemma.”
How does the false dilemma fallacy work?: The false dilemma fallacy works in two ways:

By presenting only two options as if these were the only ones available

By presenting two options as mutually exclusive (i.e., only one option can be selected or can be true at a time)

In both cases, by using the false dilemma fallacy, one conceals alternative choices and doesn’t allow others to consider the full range of options. This is usually achieved through an“either-or” construction and polarized, divisive language (“you are either a friend or an enemy”).
What is the difference between a complex question fallacy and begging the question fallacy?: The complex question fallacy and begging the question fallacy are similar in that they are both based on assumptions. However, there is a difference between them:

A complex question fallacy occurs when someone asks a question that presupposes the answer to another question that has not been established or accepted by the other person. For example, asking someone “Have you stopped cheating on tests?”, unless it has previously been established that the person is indeed cheating on tests, is a fallacy.

Begging the question fallacy occurs when we assume the very thing as a premise that we’re trying to prove in our conclusion. In other words, the conclusion is used to support the premises, and the premises prove the validity of the conclusion. For example: “God exists because the Bible says so, and the Bible is true because it is the word of God.”

In other words, begging the question is about drawing a conclusion based on an assumption, while a complex question involves asking a question that presupposes the answer to a prior question.
What is a simple definition for begging the question fallacy?: Begging the question fallacy is an argument in which you assume what you are trying to prove. In other words, your position and the justification of that position are the same, only slightly rephrased.

For example: “All freshmen should attend college orientation, because all college students should go to such an orientation.”
What is the appeal to purity fallacy?: The appeal to purity or no true Scotsman fallacy is an attempt to defend a generalization about a group from a counterexample by shifting the definition of the group in the middle of the argument. In this way, one can exclude the counterexample as not being “true,” “genuine,” or “pure” enough to be considered as part of the group in question.
Why is no true Scotsman a fallacy?: No true Scotsman arguments are fallacious because instead of logically refuting the counterexample, they simply assert that it doesn’t count. In other words, the counterexample is rejected for psychological, but not logical, reasons.
What is an example of base rate fallacy?: Suppose there is a population consisting of 90% psychologists and 10% engineers. Given that you know someone enjoyed physics at school, you may conclude that they are an engineer rather than a psychologist, even though you know that this person comes from a population consisting of far more psychologists than engineers.

When we ignore the rate of occurrence of some trait in a population (the base-rate information) we commit base rate fallacy.
Why is the appeal to authority fallacy convincing?: Appeal to authority fallacy is often convincing because of the effect authority figures have on us. When someone cites a famous person, a well-known scientist, a politician, etc. people tend to be distracted and often fail to critically examine whether the authority figure is indeed an expert in the area under discussion.
When is the appeal to authority a fallacy?: Appeal to authority is a fallacy when those who use it do not provide any justification to support their argument. Instead they cite someone famous who agrees with their viewpoint, but is not qualified to make reliable claims on the subject.
How do I identify an appeal to authority fallacy?: To identify an appeal to authority fallacy, you can ask yourself the following questions:

Is the authority cited really a qualified expert in this particular area under discussion? For example, someone who has formal education or years of experience can be an expert.

Do experts disagree on this particular subject? If that is the case, then for almost any claim supported by one expert there will be a counterclaim that is supported by another expert. If there is no consensus, an appeal to authority is fallacious.

Is the authority in question biased? If you suspect that an expert’s prejudice and bias could have influenced their views, then the expert is not reliable and an argument citing this expert will be fallacious.
What is an example of ad populum fallacy in politics?: The ad populum fallacy is common in politics. One example is the following viewpoint: “The majority of our countrymen think we should have military operations overseas; therefore, it’s the right thing to do.”

This line of reasoning is fallacious, because popular acceptance of a belief or position does not amount to a justification of that belief. In other words, following the prevailing opinion without examining the underlying reasons is irrational.
How does the ad populum fallacy work?: The ad populum fallacy plays on our innate desire to fit in (known as “bandwagon effect”). If many people believe something, our common sense tells us that it must be true and we tend to accept it. However, in logic, the popularity of a proposition cannot serve as evidence of its truthfulness.
What is the difference between ad populum fallacy and appeal to authority fallacy?: Ad populum (or appeal to popularity) fallacy and appeal to authority fallacy are similar in that they both conflate the validity of a belief with its popular acceptance among a specific group. However there is a key difference between the two:

An ad populum fallacy tries to persuade others by claiming that something is true or right because a lot of people think so.

An appeal to authority fallacy tries to persuade by claiming a group of experts believe something is true or right, therefore it must be so.
How can I identify a false cause fallacy in an argument?: To identify a false cause fallacy, you need to carefully analyze the argument:

When someone claims that one event directly causes another, ask if there is sufficient evidence to establish a cause-and-effect relationship.

Ask if the claim is based merely on the chronological order or co-occurrence of the two events.

Consider alternative possible explanations (are there other factors at play that could influence the outcome?).

By carefully analyzing the reasoning, considering alternative explanations, and examining the evidence provided, you can identify a false cause fallacy and discern whether a causal claim is valid or flawed.
What are some examples of false cause fallacy?: False cause fallacy examples include:

Believing that wearing your lucky jersey will help your team win

Thinking that everytime you wash your car, it rains

Claiming that playing video games causes violent behavior

In each of these examples, we falsely assume that one event causes another without any proof.
What is the difference between the appeal to pity fallacy and red herring fallacy?: While both the appeal to pity fallacy and red herring fallacy can serve as a distraction from the original discussion topic, they are distinct fallacies. More specifically:

Appeal to pity fallacy attempts to evoke feelings of sympathy, pity, or guilt in an audience, so that they accept the speaker’s conclusion as truthful.

Red herring fallacy attempts to introduce an irrelevant piece of information that diverts the audience’s attention to a different topic.

Both fallacies can be used as a tool of deception. However, they operate differently and serve distinct purposes in arguments.
What is argumentum ad misericordiam?: Argumentum ad misericordiam (Latin for “argument from pity or misery”) is another name for appeal to pity fallacy. It occurs when someone evokes sympathy or guilt in an attempt to gain support for their claim, without providing any logical reasons to support the claim itself. Appeal to pity is a deceptive tactic of argumentation, playing on people’s emotions to sway their opinion.
What is an example of appeal to pity fallacy?: An example of appeal to pity fallacy is the following appeal by a student to their professor:

“Professor, please consider raising my grade. I had a terrible semester: my car broke down, my laptop got stolen, and my cat got sick.”

While these circumstances may be unfortunate, they are not directly related to the student’s academic performance.
Is the planning fallacy the same as procrastination?: The planning fallacy and procrastination are not the same thing. Although they both relate to time and task management, they describe different challenges:

The planning fallacy describes our inability to correctly estimate how long a future task will take, mainly due to optimism bias and a strong focus on the best-case scenario.

Procrastination refers to postponing a task, usually by focusing on less urgent or more enjoyable activities. This is due to psychological reasons, like fear of failure.

In other words, the planning fallacy refers to inaccurate predictions about the time we need to finish a task, while procrastination is a deliberate delay due to psychological factors.
What is a real-life example of the planning fallacy?: A real-life example of the planning fallacy is the construction of the Sydney Opera House in Australia. When construction began in the late 1950s, it was initially estimated that it would be completed in four years at a cost of around $7 million.

Because the government wanted the construction to start before political opposition would stop it and while public opinion was still favorable, a number of design issues had not been carefully studied in advance. Due to this, several problems appeared immediately after the project commenced.

The construction process eventually stretched over 14 years, with the Opera House being completed in 1973 at a cost of over $100 million, significantly exceeding the initial estimates.
What is argumentum ad hominem?: Argumentum ad hominem means “argument to the person” in Latin and it is commonly referred to as ad hominem argument or personal attack. Ad hominem arguments are used in debates to refute an argument by attacking the character of the person making it, instead of the logic or premise of the argument itself.
What is the difference between a red herring fallacy and a straw man fallacy?: Although both red herring fallacy and straw man fallacy are logical fallacies or reasoning errors, they denote different attempts to “win” an argument. More specifically:

A red herring fallacy refers to an attempt to change the subject and divert attention from the original issue. In other words, a seemingly solid but ultimately irrelevant argument is introduced into the discussion, either on purpose or by mistake.

A straw man fallacy involves the deliberate distortion of another person’s argument. By oversimplifying or exaggerating it, the other party creates an easy-to-refute argument and then attacks it.
Why is the red herring fallacy a problem?: The red herring fallacy is a problem because it is flawed reasoning. It is a distraction device that causes people to become sidetracked from the main issue and draw wrong conclusions.

Although a red herring may have some kernel of truth, it is used as a distraction to keep our eyes on a different matter. As a result, it can cause us to accept and spread misleading information.
What is the difference between the sunk cost fallacy and escalation of commitment?: The sunk cost fallacy and escalation of commitment (or commitment bias) are two closely related terms. However, there is a slight difference between them:

Escalation of commitment (aka commitment bias) is the tendency to be consistent with what we have already done or said we will do in the past, especially if we did so in public. In other words, it is an attempt to save face and appear consistent.

Sunk cost fallacy is the tendency to stick with a decision or a plan even when it’s failing. Because we have already invested valuable time, money, or energy, quitting feels like these resources were wasted.

In other words, escalating commitment is a manifestation of the sunk cost fallacy: an irrational escalation of commitment frequently occurs when people refuse to accept that the resources they’ve already invested cannot be recovered. Instead, they insist on more spending to justify the initial investment (and the incurred losses).
What is a straw man argument?: A straw man argument is a distorted (and weaker) version of another person’s argument that can easily be refuted (e.g., when a teacher proposes that the class spend more time on math exercises, a parent complains that the teacher doesn’t care about reading and writing).

This is a straw man argument because it misrepresents the teacher’s position, which didn’t mention anything about cutting down on reading and writing. The straw man argument is also known as the straw man fallacy.
Why is straw man fallacy a problem?: The straw man fallacy is a problem because it occurs when we fail to take an opposing point of view seriously. Instead, we intentionally misrepresent our opponent’s ideas and avoid genuinely engaging with them. Due to this, resorting to straw man fallacy lowers the standard of constructive debate.
How to respond to a straw man fallacy?: When you are faced with a straw man fallacy, the best way to respond is to draw attention to the fallacy and ask your discussion partner to show how your original statement and their distorted version are the same. Since these are different, your partner will either have to admit that their argument is invalid or try to justify it by using more flawed reasoning, which you can then attack.
Is a slippery slope argument always a fallacy?: A slippery slope argument is not always a fallacy.

When someone claims adopting a certain policy or taking a certain action will automatically lead to a series of other policies or actions also being taken, this is a slippery slope argument.

If they don’t show a causal connection between the advocated policy and the consequent policies, then they commit a slippery slope fallacy.
How do you respond to a slippery slope fallacy?: There are a number of ways you can deal with slippery slope arguments especially when you suspect these are fallacious:

Slippery slope arguments take advantage of the gray area between an initial action or decision and the possible next steps that might lead to the undesirable outcome. You can point out these missing steps and ask your partner to indicate what evidence exists to support the claimed relationship between two or more events.

Ask yourself if each link in the chain of events or action is valid. Every proposition has to be true for the overall argument to work, so even if one link is irrational or not supported by evidence, then the argument collapses.

Sometimes people commit a slippery slope fallacy unintentionally. In these instances, use an example that demonstrates the problem with slippery slope arguments in general (e.g., by using statements to reach a conclusion that is not necessarily relevant to the initial statement). By attacking the concept of slippery slope arguments you can show that they are often fallacious.
Is ad hominem a logical fallacy?: An ad hominem (Latin for “to the person”) is a type of informal logical fallacy. Instead of arguing against a person’s position, an ad hominem argument attacks the person’s character or actions in an effort to discredit them.

This rhetorical strategy is fallacious because a person’s character, motive, education, or other personal trait is logically irrelevant to whether their argument is true or false.

Name-calling is common in ad hominem fallacy (e.g., “environmental activists are ineffective because they’re all lazy tree-huggers”).
Is appeal to ignorance a logical fallacy?: An appeal to ignorance (ignorance here meaning lack of evidence) is a type of informal logical fallacy.

It asserts that something must be true because it hasn’t been proven false—or that something must be false because it has not yet been proven true.

For example, “unicorns exist because there is no evidence that they don’t.” The appeal to ignorance is also called the burden of proof fallacy.
What is the difference between cognitive bias and logical fallacy?: People sometimes confuse cognitive bias and logical fallacies because they both relate to flawed thinking. However, they are not the same:

Cognitive bias is the tendency to make decisions or take action in an illogical way because of our values, memory, socialization, and other personal attributes. In other words, it refers to a fixed pattern of thinking rooted in the way our brain works.

Logical fallacies relate to how we make claims and construct our arguments in the moment. They are statements that sound convincing at first but can be disproven through logical reasoning.

In other words, cognitive bias refers to an ongoing predisposition, while logical fallacy refers to mistakes of reasoning that occur in the moment.
What happens in an ad hominem persuasive technique?: Ad hominem is a persuasive technique where someone tries to undermine the opponent’s argument by personally attacking them.

In this way, one can redirect the discussion away from the main topic and to the opponent’s personality without engaging with their viewpoint. When the opponent’s personality is irrelevant to the discussion, we call it an ad hominem fallacy.
What is ad hominem tu quoque?: Ad hominem tu quoque (‘you too”) is an attempt to rebut a claim by attacking its proponent on the grounds that they uphold a double standard or that they don’t practice what they preach. For example, someone is telling you that you should drive slowly otherwise you’ll get a speeding ticket one of these days, and you reply “but you used to get them all the time!”
What is the difference between the hasty generalization fallacy and anecdotal evidence fallacy?: The hasty generalization fallacy and the anecdotal evidence fallacy are similar in that they both result in conclusions drawn from insufficient evidence. However, there is a difference between the two:

The hasty generalization fallacy involves genuinely considering an example or case (i.e., the evidence comes first and then an incorrect conclusion is drawn from this).

The anecdotal evidence fallacy (also known as “cherry-picking”) is knowing in advance what conclusion we want to support, and then selecting the story (or a few stories) that support it. By overemphasizing anecdotal evidence that fits well with the point we are trying to make, we overlook evidence that would undermine our argument.
What is the opposite of the hasty generalization fallacy?: The opposite of the hasty generalization fallacy is called slothful induction fallacy or appeal to coincidence.

It is the tendency to deny a conclusion even though there is sufficient evidence that supports it. Slothful induction occurs due to our natural tendency to dismiss events or facts that do not align with our personal biases and expectations. For example, a researcher may try to explain away unexpected results by claiming it is just a coincidence.
How can you avoid a hasty generalization fallacy?: To avoid a hasty generalization fallacy we need to ensure that the conclusions drawn are well-supported by the appropriate evidence. More specifically:

In statistics, if we want to draw inferences about an entire population, we need to make sure that the sample is random and representative of the population. We can achieve that by using a probability sampling method, like simple random sampling or stratified sampling.

In academic writing, use precise language and measured phases. Try to avoid making absolute claims, cite specific instances and examples without applying the findings to a larger group.

As readers, we need to ask ourselves “does the writer demonstrate sufficient knowledge of the situation or phenomenon that would allow them to make a generalization?”
Which type of fallacy uses circular reasoning to support an argument?: Circular reasoning fallacy uses circular reasoning to support an argument. More specifically, the evidence used to support a claim is just a repetition of the claim itself. For example: “The President of the United States is a good leader (claim), because they are the leader of this country (supporting evidence)”.
What is the difference between circular reasoning fallacy and begging the question?: Although many sources use circular reasoning fallacy and begging the question interchangeably, others point out that there is a subtle difference between the two:

Begging the question fallacy occurs when you assume that an argument is true in order to justify a conclusion. If something begs the question, what you are actually asking is, “Is the premise of that argument actually true?” For example, the statement “Snakes make great pets. That’s why we should get a snake” begs the question “Are snakes really great pets?”

Circular reasoning fallacy, on the other hand, occurs when the evidence used to support a claim is just a repetition of the claim itself. For example, “People have free will because they can choose what to do.”

In other words, we could say begging the question is a form of circular reasoning.
What is an example of non sequitur?: An example of a non sequitur is the following statement:

“Giving up nuclear weapons weakened the United States’ military. Giving up nuclear weapons also weakened China. For this reason, it is wrong to try to outlaw firearms in the United States today.”

Clearly there is a step missing in this line of reasoning and the conclusion does not follow from the premise, resulting in a non sequitur fallacy.
What is the difference between the post hoc fallacy and the non sequitur fallacy?: The difference between the post hoc fallacy and the non sequitur fallacy is that post hoc fallacy infers a causal connection between two events where none exists, whereas the non sequitur fallacy infers a conclusion that lacks a logical connection to the premise.

In other words, a post hoc fallacy occurs when there is a lack of a cause-and-effect relationship, while a non sequitur fallacy occurs when there is a lack of logical connection.
What is the difference between post hoc fallacy and hasty generalization fallacy?: Post hoc fallacy and hasty generalization fallacy are similar in that they both involve jumping to conclusions. However, there is a difference between the two:

Post hoc fallacy is assuming a cause and effect relationship between two events, simply because one happened after the other.

Hasty generalization fallacy is drawing a general conclusion from a small sample or little evidence.

In other words, post hoc fallacy involves a leap to a causal claim; hasty generalization fallacy involves a leap to a general proposition.
What is an example of post hoc fallacy?: An example of post hoc fallacy is the following line of reasoning:

“Yesterday I had ice cream, and today I have a terrible stomachache. I’m sure the ice cream caused this.”

Although it is possible that the ice cream had something to do with the stomachache, there is no proof to justify the conclusion other than the order of events. Therefore, this line of reasoning is fallacious.
How can I identify a post hoc fallacy?: When someone uses an argument that claims there is a causal connection between two events, you can take the following steps to determine whether this is a post hoc fallacy:

Is the causal connection presented as an absolute truth or as a possibility? Absolute statements often signal a leap in logic.

Do they have evidence to back up their claim, other than the chronological order of events? If not, it is a case of post hoc fallacy.

When in doubt, ask the other person to elaborate on their reasoning and offer supporting evidence.
What is the opposite of the fallacy of composition?: The opposite of the fallacy of composition is the fallacy of division. In the fallacy of division, the assumption is that a characteristic which applies to a whole or a group must necessarily apply to the parts or individual members. For example, “Australians travel a lot. Gary is Australian, so he must travel a lot.”
What is the difference between the fallacy of composition and hasty generalization fallacy?: The fallacy of composition is similar to and can be confused with the hasty generalization fallacy. However, there is a difference between the two:

The fallacy of composition involves drawing an inference about the characteristics of a whole or group based on the characteristics of its individual members.

The hasty generalization fallacy involves drawing an inference about a population or class of things on the basis of few atypical instances or a small sample of that population or thing.

In other words, the fallacy of composition is using an unwarranted assumption that we can infer something about a whole based on the characteristics of its parts, while the hasty generalization fallacy is using insufficient evidence to draw a conclusion.
What is cost-benefit fallacy?: Cost-benefit fallacy is a common error that occurs when allocating sources in project management. It is the fallacy of assuming that cost-benefit estimates are more or less accurate, when in fact they are highly inaccurate and biased. This means that cost-benefit analyses can be useful, but only after the cost-benefit fallacy has been acknowledged and corrected for. Cost-benefit fallacy is a type of base rate fallacy.

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