Fallacy Friday!

Today's Logical Fallacy is...Shifting the Burden of Proof!

(related to “appeal to ignorance”) This fallacy occurs when the burden of proof is placed on the wrong side of an argument. In a logical...

Friday, January 15, 2016

Today's Logical Fallacy is...Correlation Equals Causation!

(False Cause, Post Hoc or Faulty Causality, or Correlation vs. Causation; post hoc ergo propter hoc)

A very common fallacy both in everyday usage and in formal arguments, this fallacy occurs when someone confuses “correlation” (when things occur at the same time or immediately after one another) with “causation” (when one thing causes another). It is a mistake to assume that the order of events means that one event caused the other for there are many variables that could contribute to the pattern we see. Not only could the pattern be a pure coincidence, it is most often due to a common “third” cause of both events. Statistics play an important role in this fallacy. Many will see a figure and automatically draw a conclusion without thinking of what may have been left out.

This fallacy does not mean that statistical conclusions can be disregarded as a correlation/causation fallacy (another fallacy known as the “denial of causation” fallacy.) The reason this is a fallacy is not because a conclusion is drawn from data but because the data doesn’t include all the possible variables. It would be incorrect to dismiss statistical evidence if it were gathered from a controlled experiment in which the purpose is to control for other potential variables (e.g. a pharmaceutical study). Even if the statistics did come from a collection of data, it is still possible to draw a valid conclusion if you look at multiple independent correlations (i.e. radiometric dating, a process that uses multiple radioactive isotopes, samples, and sites from which those samples are taken).


In the 1990’s, religious attendance and illegal drug use both rose. Therefore, religious attendance caused illegal drug use. (Or illegal drug use resulted in more people feeling the need to attend church.) (Third alternative may be that both rose due to an increase in societal unrest.)

A black cat crossed Babbs' path yesterday and, sure enough, she was involved in an automobile accident later that same afternoon.

Many people get rich when they pray for wealth, but many people who never pray also get rich, and many people who pray to get rich stay poor; also, what about people who pray to other gods and get rich?

Drinkers are more likely than non-drinkers to get lung cancer, suggesting drinking causes lung cancer. (It turns out there is a strong correlation between consuming alcohol and developing lung cancer. The post hoc fallacy would be asserting that alcohol consumption causes lung cancer; the actual reason is that people who drink more also tend to smoke, or smoke more, than non drinkers.)

Many claim that marijuana is a “gateway drug” because those who have smoked marijuana are more likely than those who haven’t to go on to try other drugs. The post hoc fallacy would be asserting that marijuana use leads to increased use of other drugs; the more logical explanation is that those who are willing to try one drug are obviously also willing to try other drugs: the cause – willingness to try or use drugs – must necessarily exist before one tries pot; otherwise, you wouldn’t try it in the first place.

I got better after just a couple of days of taking cold medicine. Therefore, the cold medicine cured me of my cold (reality: colds usually only last a couple of days anyway).

As the number of priests in America has risen, so has the amount of alcoholism. Therefore, priests are alcoholics (or priests cause alcoholism).

There has been a strong correlation in the 20th century of a strong correlation between the number of radios and the number of people in insane asylums (reality: most likely independent events).

Global warming has increased as the number of pirates has decreased. This is because the pirates are the original “Pastafarians” and are “absolute divine beings,” and, due to our disrespect of them, the Flying Spaghetti Monster is punishing us.

There is a strong correlation between the amount of serious crime committed and the amount of ice cream sold by street vendors. Therefore, criminals love ice cream. (reality: both increase with temperature).

The more firemen are sent to a fire, the more damage is done.

As the number of ice cream sales increase, so does the number of shark attacks. Therefore, sharks prefer people who have recently eaten ice cream (reality: both increase with temperature – more people in the water for the sharks to attack).

Mortality rates decrease with the number of televisions per capita. Therefore, TVs will keep people from dying (reality: both are due to gross domestic product).

“For example, it was observed that cigarette smoking correlates with getting lung cancer. The tobacco industry, invoking the ‘correlation is not causation’ logical fallacy, argued that this did not prove causation. They offered as an alternate explanation ‘factor x’, a third variable that causes both smoking and lung cancer. But we can make predictions based upon the smoking causes cancer hypothesis. If this is the correct causal relationship, then duration of smoking should correlate with cancer risk, quitting smoking should decrease cancer risk, smoking unfiltered cigarettes should have a higher cancer risk than filtered cigarettes, etc. If all of these correlations turn out to be true, which they are, then we can triangulate to the smoking causes cancer hypothesis as the most likely possible causal relationship and it is not a logical fallacy to conclude from this evidence that smoking probably causes lung cancer” (theskepticsguide.org).

"Here's some simple logic....allergies have been on the rise in children for years...therefore children's allergic/negative reactions to vaccines are also on the rise...therefore more parents, in doing what's best for their child...are not vaccinating or are taking a slower/ different route in getting them vaccinated."

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