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The History of 'Correlation Does Not Imply Causation'

Soulskill posted about 2 years ago | from the does-not-imply-godwin-either dept.

Stats 223

Dr Herbert West writes "The phrase 'correlation does not imply causation' goes back to 1880 (according to Google Books). However, use of the phrase took off in the 1990s and 2000s, and is becoming a quick way to short-circuit certain kinds of arguments. In the late 19th century, British statistician Karl Pearson introduced a powerful idea in math: that a relationship between two variables could be characterized according to its strength and expressed in numbers. An exciting concept, but it raised a new issue: how to interpret the data in a way that is helpful, rather than misleading. When we mistake correlation for causation, we find a cause that isn't there, which is a problem. However, as science grows more powerful and government more technocratic, the stakes of correlation — of counterfeit relationships and bogus findings — grow larger."

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Maybe (5, Funny)

mgrivich (1015787) | about 2 years ago | (#41529643)

Re:Maybe (5, Funny)

jcwayne (995747) | about 2 years ago | (#41529831)

Then there's this: http://xkcd.com/925/ [xkcd.com]

Re:Maybe (4, Funny)

nharmon (97591) | about 2 years ago | (#41530023)

After that, I started holding laptops exactly like that, making people cringe. True story.

Re:Maybe (3, Interesting)

DeTech (2589785) | about 2 years ago | (#41530117)

I love how these 2 XKCD's (esp. the mouse over text) summarize the entire content of the comments below.

Re:Maybe (1)

Skewray (896393) | about 2 years ago | (#41530121)

So the conclusion is that the phrase in question causes an increase in available correlations? Interesting.

Re:Maybe (2)

jmerlin (1010641) | about 2 years ago | (#41530917)

I just drew a similar graph. plotting global warming against piracy. I have concluded that global warming causes piracy, and in turn, piracy causes global warming.

Now, to get the RIAA to become constructive, we should point out that solving global warming will necessarily solve piracy.

Re:Maybe (1)

dkleinsc (563838) | about 2 years ago | (#41530679)

There's also this correlation (not xkcd, but still awesome):
Global Average Temperature vs Number of Pirates [venganza.org]

The number of pirates skyrocketed in late 1999 (1)

tepples (727027) | about 2 years ago | (#41530723)

The number of pirates skyrocketed starting in the fourth quarter of 1999 when Napster kicked off the culture of illegal peer-to-peer file sharing, yet there hasn't been too much of a cooling effect. Correlation busted.

Correlation != causation. (1)

140Mandak262Jamuna (970587) | about 2 years ago | (#41529651)

However, as science grows more powerful and government more technocratic, the stakes of correlation — of counterfeit relationships and bogus findings — grow larger."

Well is science growing powerful finds all these false correlations? Or these correlations always existed and now we know enough to say they were false. Anyway correlation is not causation.

Re:Correlation != causation. (2)

flaming error (1041742) | about 2 years ago | (#41529837)

Who says the correlations are false? Relationships besides A->B do exist.

Re:Correlation != causation. (5, Insightful)

Anonymous Coward | about 2 years ago | (#41529853)

How about Correlation is insufficient to PROVE causation

Re:Correlation != causation. (0)

Anonymous Coward | about 2 years ago | (#41530197)

And instead of saying "causation," we all say "causality," so we don't sound like a bunch of third-grade hillbillies. If the word "causality" is good enough for my elementary stats professor, it's good enough for us.

-- Ethanol-fueled

Re:Correlation != causation. (1)

Jeremiah Cornelius (137) | about 2 years ago | (#41530345)

WHAT!

Your hillbillies made it to THIRD GRADE!?

If correlation WERE causality, then I'd ascribe this occurrence as a sign for the end-of-times.

Re:Correlation != causation. (3, Insightful)

Lord Bitman (95493) | about 2 years ago | (#41530003)

The correlations are NOT "false". The relationships between the numbers are (almost always) NOT "conterfeit".

"Correlation does not imply causation" means exactly that. If the sky is dark and people are carrying around umbrellas, this does NOT imply that darkness causes umbrellas, or that umbrellas cause darkness. The causal relationship between two numbers is not determined by how often one number changes at the same time as another.

To put it another way: correlation is an *observed* behaviour, causation is a *tested* behaviour.

Re:Correlation != causation. (1)

vlm (69642) | about 2 years ago | (#41530125)

To put it another way: correlation is an *observed* behaviour, causation is a *tested* behaviour.

Nice, but how bout correlation is a math formula, on the other hand causation has a ten page philosophical wikipedia page and even though Hume died like 300 years ago this year people are still arguing about it, with the exception that on the internet everyone agrees correlation isn't it, which I guess is at least some progress.

Re:Correlation != causation. (5, Interesting)

jellomizer (103300) | about 2 years ago | (#41530157)

Correlation may not lead to causation... However it tends to give a clue on the causation.

For example a Correlation between the number of tattoos vs. the number of Motorcycle accidents.
Well ink in your skin doesn't cause you to get in an accident. However people who are more apt to taking risks will more likely get a tattoo. People who take more risks get into accidents more.

In terms of policy, you want to reduce motorcycle accidents, telling people you need to stop getting tattoos will not be effective. However with this correlation you may get results by posting motorcycle safety information at the tattoo parlors.

But using Correlation != causation as a way to short circuit an argument isn't that effective. Because if your goal is to dig for the truth or a solution, the correlation is important, and if the correlation seems reasonable to create the causation it is worth further investigation.

Correlation implies utility of search for cause (1)

tepples (727027) | about 2 years ago | (#41530819)

Well is science growing powerful finds all these false correlations?

Think of it this way: When you find a correlation, there are four possibilities: A causes B, B causes A, C causes A and B, or chance. Repeating experiments helps strengthen the correlation, which diminishes the probability of chance. Further experiments varying those parts of A and B that can be controlled help distinguish among the remaining three and help identify C.

Science grows more powerful? (2)

sackvillian (1476885) | about 2 years ago | (#41529661)

In what sense, exactly does science grow more powerful? In my experience, sciences grows more expensive, less funded, more hyped, less understood, and overall less heeded.

Re:Science grows more powerful? (4, Informative)

flaming error (1041742) | about 2 years ago | (#41529769)

> In what sense, exactly does science grow more powerful?

Space Stations. Tsunami warning systems. Earthquake warning systems. Cochlear implants. Big Dog. Spirit & Opportunity. Curiosity. Exoplanets. Higgs Boson.

Re:Science grows more powerful? (-1)

Anonymous Coward | about 2 years ago | (#41529771)

In what sense, exactly does science grow more powerful? In my experience, sciences grows more expensive, less funded, more hyped, less understood, and overall less heeded.

Quit complaining and sit down, Poindexter.

Re:Science grows more powerful? (2)

i kan reed (749298) | about 2 years ago | (#41529797)

Science grows more powerful as an explanatory tool as we grasp more of the world around us. Philosophical or logical power.

If you have premise p which is "science", the set of things you can derive or contradict from that grows quite rapidly.

Re:Science grows more powerful? (1)

Nyder (754090) | about 2 years ago | (#41529829)

In what sense, exactly does science grow more powerful? In my experience, sciences grows more expensive, less funded, more hyped, less understood, and overall less heeded.

Cosmic & Gamma rays dude. Don't you read Marvel Comics?

Re:Science grows more powerful? (1)

Anonymous Coward | about 2 years ago | (#41529877)

As more and more scientists assume the role of advocate instead of researcher and adviser, the institution of science becomes more influential in society.

Even now, entire countries base some public policy on input from organizations that cloak themselves in Science.

The idea of a Carbon tax was not something dreamed up in a smoke filled room somewhere. It was the product of science and has been treated as unassailable buy many parts of society because of its origin.

Re:Science grows more powerful? (3, Informative)

scamper_22 (1073470) | about 2 years ago | (#41529901)

We're the most scientific society the world has ever known.
Science holds more power today that at any point in history.

Now you can say, it is 'not true science' in as much as people can say Saudi Arabia or Iran is not 'true Islam'.

Some abstract notion of science or religion as *truth*.

But back in reality.

People who say science is their guide are at the most powerful in history. Regular people walk around saying 'we need independent scientific bodies to set healthcare, education policy. People readily accept the truth from scientific panels without much understanding of the actual science. Institutions of science are well funded by government as is the education systems (Relative to most other times in history).

Re:Science grows more powerful? (0)

Anonymous Coward | about 2 years ago | (#41530605)

Your "glass is half full" assessment is a way out of place here, stranger. ;)

Re:Science grows more powerful? (0)

vlm (69642) | about 2 years ago | (#41529981)

In what sense, exactly does science grow more powerful?

In how liberal arts grads, especially journalists, can be completely ignorant of the scientific method, leading to an article with really weird logic, at least from a scientific perspective.

Correlation is incredibly handy to at least initially point the way to a possible scientific model or theory that can be used to make useful falsifiable predictions about the future. But don't confuse the map with the terrain. Its a compass thats often broken, not a GPS unit.

Causation is a pretty fuzzy philosophical topic so arguing about what it is or isn't, is not terribly useful.

Maybe the best way to explain it to a liberal arts grad would be something like the journey is different than the destination, or when you come to a fork in the road and see the road less traveled correlation is how you know its less traveled, or that its all somehow symbolic of Hemmingways Old Man And The Sea and the act of fishing is much different than the expectations about getting a fish. Either that or the point of Joyce's Ulysses wasn't a numerical analysis that people walked around a hell of a lot in Ireland a hundred years ago. Now look at how the liberal arts guys are going to laugh at my pitiful attempt at swimming with their big literary fish... note to lib arts folks... that superior laughing feeling is what the STEM people experience when algebra dropouts try to swim in our sea of math... so when the smart guy says something about statistics, if the 1040EZ form baffles you and you can't find the "any" key on your keyboard, thats a good sign you should probably shut up and do what the smart guy says. Harsh, but that's reality, sometimes.

More powerful science, less Impedence? (2)

TiggertheMad (556308) | about 2 years ago | (#41530563)

Causation is a pretty fuzzy philosophical topic so arguing about what it is or isn't, is not terribly useful.

It seems pretty simple to me. Correlation is 'Sometimes A and B are found together'. Causation is 'A causes B'. But go on...

Maybe the best way to explain it to a liberal arts grad would be something like the journey is different than the destination

...I guess. So we are telling them that Correlation and Causation have close to the same meaning, got it. Like ham isn't bacon, and yet both are strangely delicious. Mmmmmm, pig meat...sorry, go on.

or when you come to a fork in the road and see the road less traveled correlation is how you know its less traveled,

Wait, what?

or that its all somehow symbolic of Hemmingways Old Man And The Sea and the act of fishing is much different than the expectations about getting a fish.

Is this stats 101, or literary criticism 204?

Either that or the point of Joyce's Ulysses wasn't a numerical analysis that people walked around a hell of a lot in Ireland a hundred years ago.

....I am getting more and more confused. Goddam Irish.

.. note to lib arts folks... that superior laughing feeling is what the STEM people experience when algebra dropouts try to swim in our sea of math...

STEM == Science Engineering Technology Math, I am guessing. For just a moment as I read that, I thought you were talking about some alien genetically engineered clones grown from stem cells, bent on subverting and destroying our society from with in. Too bad really, because it would have tied up the explanation nicely.

so when the smart guy says something about statistics, if the 1040EZ form baffles you and you can't find the "any" key on your keyboard, thats a good sign you should probably shut up and do what the smart guy says.

...And you win them over with your swauve, charming wit. SLAMDUNK!

Please promise me that you will never become a school teacher

Re:Science grows more powerful? (1)

inertialFrame (259221) | about 2 years ago | (#41530009)

So far as I can tell, science grows more powerful in each of two different but interrelated ways.

1. As the experimental data come in, the theories must change so that they accurately predict the results from an ever wider set of experimental circumstances.

2. Occasionally, there is a theoretical improvement that both increases the range of predicted circumstances and simplifies at some level the overall conceptual framework.

So long as civilization does not altogether collapse, and the various scientific communities along with it, neither of these two senses of scientific accomplishment depends on funding, but the rate at which science becomes more powerful does depend on funding.

Re:Science grows more powerful? (0)

Anonymous Coward | about 2 years ago | (#41530151)

I took this to mean science is more powerful as a way of convincing something is true in popular culture.
Eg. The man in the white lab coat says this diet is 89% effective. Science has spoken!

fundamental (1)

markian (745705) | about 2 years ago | (#41529705)

Is this correlated with the fundamental interconnectedness of all things?

Re:fundamental (3, Funny)

JustOK (667959) | about 2 years ago | (#41529809)

It caused it.

Re:fundamental (1)

Antipater (2053064) | about 2 years ago | (#41529935)

Nonsense. I was already interconnected with your mother; the "all other things" bit was merely coincidental.

Re:fundamental (1)

vlm (69642) | about 2 years ago | (#41530173)

Nonsense. I was already interconnected with your mother; the "all other things" bit was merely coincidental.

You're missing a fairly obvious joke about the causational result of him being able to say "I think therefore I am" leading to centuries of mistaken mind-body dualism, aka "whos your daddy"

Re:fundamental (1)

fibonacci8 (260615) | about 2 years ago | (#41530195)

So you're a fan of "Fifty Shades of Grey".

Re:fundamental (1)

JustOK (667959) | about 2 years ago | (#41530215)

Thank God you responded. The CDC needs to contact you about the...well, you know. Mom couldn't remember your name, just that you had a remarkably small wee-wee.

On the other hand ... (4, Funny)

fahrbot-bot (874524) | about 2 years ago | (#41529717)

... and is becoming a quick way to short-circuit certain kinds of arguments.

... Correlation does not imply causation.

Re:On the other hand ... (3, Funny)

Tackhead (54550) | about 2 years ago | (#41529975)

... and is becoming a quick way to short-circuit certain kinds of arguments.

... Correlation does not imply causation.

The decline in classical education standards is, however, a causal factor behind the shift from references to the "post hoc ergo propter hoc fallacy" towards references to the phrase "correlation does not imply causation".

Re:On the other hand ... (0)

Anonymous Coward | about 2 years ago | (#41530193)

... and is becoming a quick way to short-circuit certain kinds of arguments.

... Correlation does not imply causation.

The decline in classical education standards is, however, a causal factor behind the shift from references to the "post hoc ergo propter hoc fallacy" towards references to the phrase "correlation does not imply causation".

Did you mean "cum hoc ergo propter hoc"?

Re:On the other hand ... (1)

SomePgmr (2021234) | about 2 years ago | (#41530867)

I think his point is the same in either case. "Post hoc" is "after this, therefore because of this" and the other is "with this..." A and B are observationally correlated in both - one just indicates a chronological order.

"Post hoc" is just the one we all had to know to get through middle school. :)

Re:On the other hand ... (1)

Cinder6 (894572) | about 2 years ago | (#41529987)

It does imply causation. It doesn't prove it, which is why saying that cause is there is irresponsible. Correlation merely states that one thing might cause another, so further study may be warranted.

Re:On the other hand ... (1)

Cinder6 (894572) | about 2 years ago | (#41530071)

I suppose I should mention I'm using the definition of "imply" that means "suggest"; as has been mentioned below me, "imply" has different meaning in mathematics.

The key word is "prove" (5, Insightful)

argStyopa (232550) | about 2 years ago | (#41529751)

Correlation doesn't PROVE causation.... ...but it bloody well DOES suggest it, at least in the course of our daily lives.

The reason this phrase is so catchy is that it's counter-intuitive, and easily proven to be true. People love to use it as a "gotcha" phrase, PRECISELY because in regular life correlation does in fact usually imply causation.

In fact, correlation is used by most scientists to begin the hypothesis process. A power plant is built on a river, and the river starts drying up - most people would begin their analysis by checking on the power plant, and not the population of honeybees.

Your kid is alone in the kitchen. The cookie jar is (now) empty. Does his presence CONCLUSIVELY PROVE that he ate the cookies? Of course not, and a wise parent would find other evidence to draw a conclusion. But the correlation of their places in time and space, as well as a known predilection for cookies means that correlation strongly suggests an avenue of investigation (you're probably not going to start figuring out what happened by pursuing some other entirely different course).

It's the sort of empty-headed 'gotcha' phrase that's so popular and so often used without real thought behind it.

Re:The key word is "prove" (1)

Daniel_Staal (609844) | about 2 years ago | (#41529847)

The main problem that the phrase attempts to solve these days is with data-mining. If you have a huge dataset, and start pulling random trends out of it, there's a decent likelihood that some of those trends will correlate. But you have no real evidence that one caused the other - the correlation is just as likely to be random chance. You didn't start by finding a problem which you need to find a cause for: you started with 'What's going on?' You found that out, but it's tempting to start assigning problems, causes, and solutions because you think you can.

Re:The key word is "prove" (0)

Anonymous Coward | about 2 years ago | (#41530239)

Trying to solve a stupid action (jumping to a conclusion) by creating a catchy, but stupidly wrong, phrase doesn't help.

Re:The key word is "prove" (1)

Anonymous Coward | about 2 years ago | (#41530279)

Correlation is sometimes just as good as causation. For example there's a strong correlation between being an iPhone user and spending more on apps. However, purchasing an iPhone doesn't *cause* you to buy any additional apps at all. The causes of that phenomenon are likely knowable but I don't really care about them. But as a person who makes mobile apps as part of their job I tend to focus first on iOS and then later Android if the product becomes successful.

Re:The key word is "prove" (0)

Anonymous Coward | about 2 years ago | (#41530779)

However, purchasing an iPhone doesn't *cause* you to buy any additional apps at all. The causes of that phenomenon are likely knowable but I don't really care about them.

There are no causes at all for the cited phenomenon--I know this is somewhat off-topic here, but if you're confusing different kinds of reason, it's time to read Schopenhauer's On the Fourfold Root of the Principle of Sufficient Reason (yeah, I had to kinda wikipedia the translated title because I only read it in its original language ...).

A catchy little book, would help in many superfluous discussions about false conclusions from unclear wording on causes, reasons, grounds, ...

Re:The key word is "prove" (1)

Hentes (2461350) | about 2 years ago | (#41530627)

Exactly, this is a very big problem with social "sciences" that are almost purely empirical and the only theory they know (in the good case) is statistics. Without a theoretical foundation it's almost impossible to detect when correlation is misleading: the 95% rule is not a replacement for a scientific model. When a physics experiment yield results suggesting faster-than-light particles scientists knew that it was likely an error because of the field's theoretical background. These checks aren't present in most soft sciences.

Re:The key word is "prove" (1)

John_3000 (166166) | about 2 years ago | (#41529867)

Well said.

Roughly, if A and B are correlated then either A causes B or B causes A or both A and B are caused by some C.

So causation is implied in every case! :-)

Re:The key word is "prove" (0)

Anonymous Coward | about 2 years ago | (#41529931)

Or A and B happened at the same time purely by coincidence or random chance, and no causation exists to be found.

Re:The key word is "prove" (1)

Comboman (895500) | about 2 years ago | (#41530005)

In that case, C = coincidence or random chance.

Re:The key word is "prove" (0)

Anonymous Coward | about 2 years ago | (#41530297)

Two events happening at the same time is not a correlation. However, two things that *often* happen together might be.

Repeat experiment (1)

tepples (727027) | about 2 years ago | (#41530907)

That's why experiments are repeated: to make the probability of chance smaller.

Re:The key word is "prove" (1)

mcgrew (92797) | about 2 years ago | (#41530367)

Or it's simply coincidence.

The key word is "Correlation" (4, Informative)

flaming error (1041742) | about 2 years ago | (#41529899)

Correlation suggests only Correlation. It doesn't suggest causation, but as you noted, it does suggest areas for further investigation. The relationship may or may not turn out to be directly causal.

Re:The key word is "Correlation" (1)

Instantlemming (816917) | about 2 years ago | (#41530101)

Global warming and the decline of pirates comes to mind.
Also, http://cats-or-dogs.com/ [cats-or-dogs.com] is a nice study of correlations...

Re:The key word is "Correlation" (1)

Daniel Dvorkin (106857) | about 2 years ago | (#41530331)

Notice how very few of the correlations that turn up are statistically significant? That should tell you something: a statistically significant correlation (and if you're looking at a bunch of possible correlations at once, your bar for significance should be pretty high) usually does mean there's some kind of causal relationship somewhere, whether it's A causing B, B causing A, or some unmeasured C causing both.

Re:The key word is "Correlation" (1)

timeOday (582209) | about 2 years ago | (#41530817)

What you just said is all circular. "Statistically significant" has no other meaning than "probably not coincidental."

Re:The key word is "Correlation" (2)

MrHanky (141717) | about 2 years ago | (#41530431)

Global warming and the decline of pirates was mostly about the correlation between the will to ignore one set of facts [epa.gov] with the enthusiasm for ignoring another set of facts [wikipedia.org] .

Re:The key word is "prove" (1)

zolltron (863074) | about 2 years ago | (#41529995)

The reason this phrase is so catchy is that it's counter-intuitive, and easily proven to be true. People love to use it as a "gotcha" phrase, PRECISELY because in regular life correlation does in fact usually imply causation.

I agree, and this cannot be overstated. I worry that the use of this phrase is almost more dangerous than the mistaken belief that correlation does imply causation.

To be precise, in most of the examples people love to trot out, correlation does imply causation, just not direct causation. A and B might be correlated because they are both caused by the same thing. While a correlation between obesity and TV watching doesn't imply that TV watching causes obesity, the correlation is good evidence that one causes the other or that there is a third thing, laziness perhaps, that causes both.

Of course there are counter examples to this assumption, called Reichenbach's principle [stanford.edu] , but they are even more rare.

Re:The key word is "prove" (2)

arth1 (260657) | about 2 years ago | (#41530021)

Your kid is alone in the kitchen. The cookie jar is (now) empty. Does his presence CONCLUSIVELY PROVE that he ate the cookies?

Um, where's the correlation here?

Presence of a kid in the kitchen correlates inversely to number of cookies in jar?
Why, then the conclusion is obvious - a dearth of cookies causes kids.

Re:The key word is "prove" (0)

Anonymous Coward | about 2 years ago | (#41530025)

It's the sort of empty-headed 'gotcha' phrase that's so popular and so often used without real thought behind it.

Exactly. The short version is this: causation is irrelevant if you're just trying to use one variable as a heuristic to detect or determine the probable value of another. You only need correlation [wikipedia.org] for that.

"Causation" (look at the word: "cause") is only relevant if you're actually trying to prove some sort of cause and effect relationship.

Re:The key word is "prove" (0)

Anonymous Coward | about 2 years ago | (#41530031)

The moment someone calls out that correlation does not imply causation, they have de facto admitted the correlation IS the causation.

Poor example - or not (1)

gr8_phk (621180) | about 2 years ago | (#41530167)

Your kid is alone in the kitchen. The cookie jar is (now) empty. Does his presence CONCLUSIVELY PROVE that he ate the cookies? Of course not, and a wise parent would find other evidence to draw a conclusion. But the correlation of their places in time and space, as well as a known predilection for cookies means that correlation strongly suggests an avenue of investigation (you're probably not going to start figuring out what happened by pursuing some other entirely different course).

The kid there at the time, when the cookie jar is empty implies NOTHING. Perhaps the kid is still standing around wondering what to snack on precisely BECAUSE the cookie jar is empty. You correctly identify and avenue of investigation only by pointing out that the kid has a predilection for cookies - if that were not the case, his presence in the kitchen would be irrelevant. If the other kid upstairs liked cookies and this one hates that kind of cookie, you would not say their presence together is supportive of the hypothesis that he ate them - you'd go see what the other kid is munching upstairs.

And this very nicely illustrates the point of why it's unintuitive.

Re:The key word is "prove" (0)

Anonymous Coward | about 2 years ago | (#41530185)

The cookie jar story is not correlation. That's inferring a narrative explanation from a conclusion relative to your subjective perception of the likelihood of various premises that lead to that conclusion. Subjective is the operative word. You could more rigorously characterize this as a Bayesian process of starting from guesses at the likelihood of different causes, but the reality is that your brain dispenses with the rigor and just lets its tangle of neurons spit out an answer.

Correlation doesn't come into it because there isn't a data set. You just have your internal mishmash of perceptions of different circumstances and even that gets filtered through more subjective weights in a sort of relevance filter. This is something that produces not terribly inaccurate conclusions a fairly decent amount of the time, which is actually a pretty good accomplishment considering the nature of the universe, but its not really comparable to the kind of reasoning you should use when you're trying to make objective predictions based on hard data.

Re:The key word is "prove" (1)

jemenake (595948) | about 2 years ago | (#41530213)

Correlation doesn't PROVE causation.... ...but it bloody well DOES suggest it,

... or it could suggest that there's a third cause, right? Like when Steven Leavitt mentions that people used to think that ice-cream caused polio because of some correlation. Turns out that the correlation was due to the fact that, when it got hot in the Summer, people would: 1) eat ice-cream and 2) go swim at the local swimming hole (where they'd get polio).

Now, I take it that your point (about the "suggestion" of causation) is that it gives us reason to pursue, further, investigation into a possibly link between two things, but I'd phrase it a different way. I'd say that correlation shows that we cannot, yet, rule out causation. In other words, if we find NO correlation, then there's not going to be any causation, and we can all go home. If we, however, DO find correlation, then we can't rule causation out, so we gotta keep going.

Your kid is alone in the kitchen. The cookie jar is (now) empty. Does his presence CONCLUSIVELY PROVE that he ate the cookies?

When phrased this way, there's little implication of causality. The problem is when a headline reads "Depressed people send more emails". Now, it didn't say anything about "causing" anything, but... let's turn the sentence around: "People who send lots of emails are more depressed".

From a logic point of view, those two statements are fairly identical. So, how come they don't feel the same when we read them? I argue that it's because we have some tendency to infer that the former caused the latter... for whatever reason. So, I'd argue that the knee-jerk "correlation doesn't prove causation" people are merely trying to quash this innate tendency to assume causation.

Re:The key word is "prove" (0)

Anonymous Coward | about 2 years ago | (#41530271)

I think in fact, correlation often doesn't imply causation. But most of the examples of where it doesn't are so obvious that we ignore them. Does wearing a skirt cause someone to have long hair? I don't think so.

Re:The key word is "prove" (1)

poity (465672) | about 2 years ago | (#41530285)

It only suggests a simultaneous occurrence. If B happens when A happens, it may be that A causes B, but it could just as likely that an unknown C is the cause of both A and B. We can only say that there is a relationship, and that an observed change in A can help us better predict a change in B, nothing more.

Re:The key word is "prove" (1)

Frequency Domain (601421) | about 2 years ago | (#41530327)

Correlation doesn't PROVE causation.... ...but it bloody well DOES suggest it, at least in the course of our daily lives.

The reason this phrase is so catchy is that it's counter-intuitive, and easily proven to be true. People love to use it as a "gotcha" phrase, PRECISELY because in regular life correlation does in fact usually imply causation.

No, you have it exactly backwards. Causation usually implies correlation(*). But there are lots of correlations that are not in any way causally related, such as a) the decline in piracy and increase in global temperatures in the past two centuries; b) the rabbit population in Australia and the performance of the London stock exchange for the past century; or c) the monthly per capita consumption rate of ice cream and the monthly per capita rate of drowning deaths for seaside locations north of 40 degrees latitude. The first two are because both sets of observations have changed in consistent fashions over time. The third is because people seek/avoid both swimming and ice cream based on seasonal variations of temperature, i.e., there's what's called a "lurking covariate". In none of these cases does one of the sets of observations cause the other. You won't change global warming by encouraging piracy, swing the stock market by raising rabbits in Oz, or change drowning statistics by banning ice cream.

(*) Causation is not always associated with correlation, because correlation measures tendency towards a linear fit. If there's a non-linear relationship, you can have perfect causality and zero correlation. Example - Let X be uniformly distributed between -1 and 1, and let Y = X^2. If I tell you a particular X value you can predict Y perfectly, but if you work the math of correlation you'll find Corr(X,Y) = 0.

Re:The key word is "prove" (0)

Anonymous Coward | about 2 years ago | (#41530545)

"Correlation doesn't PROVE causation.... ...but it bloody well DOES suggest it, at least in the course of our daily lives."

Only in trivial cases, the more non-trivial the harder it gets. There's many types of correlation, correlation is a big catch all word that captures many instances of different kinds of reasoning.

Re:The key word is "prove" (1)

Kjella (173770) | about 2 years ago | (#41530825)

I think you've drawing the conclusion the wrong way, because we have a vague idea of the causal relationship the correlation is collaborative evidence. There's lots and lots of things that correlate that my mind dismisses because it's absurd or there's obviously an underlying cause for it. I would say my investigation of the missing cookies would be far more causal - "Why are they gone? Probably because someone has eaten them. Who likes cookies? Who had access to the cookies? Who do I know has been in their presence recently?" Or as a prosecutor would say it: Motive, means and opportunity. I'd not go into any random correlation, like it was sunny outside when the cookies were here, now it's night and they're gone. Because even though it's clearly correlated, it's absurd that the sunset stole my cookies.

Causation was a tool of the Nazis. (5, Funny)

EvilNTUser (573674) | about 2 years ago | (#41529799)

The people who mindlessly deny the possibility of causation are worse than those who compare everything to Hitler.

Re:Causation was a tool of the Nazis. (1)

jcwayne (995747) | about 2 years ago | (#41529855)

Apparently today's Godwin number is 10.

Re:Causation was a tool of the Nazis. (1)

EvilNTUser (573674) | about 2 years ago | (#41529941)

I could've gotten first post if it wasn't for those damned Nazis.

Re:Causation was a tool of the Nazis. (0)

Anonymous Coward | about 2 years ago | (#41529917)

Plonk. You lost.

Re:Causation was a tool of the Nazis. (4, Funny)

arth1 (260657) | about 2 years ago | (#41529927)

The people who mindlessly deny the possibility of causation are worse than those who compare everything to Hitler.

Funny you should say that. My recent studies have led me to the conclusion that being a vegetarian causes you to become a bad painter.

We need to make a new phrase popular (2)

pla (258480) | about 2 years ago | (#41529887)

and is becoming a quick way to short-circuit certain kinds of arguments

The real problem here comes from people using that as a "short cut" to an actual argument.

On the one hand, we've done a great job at getting them to grasp that correlation does not imply causation. Now, we need to get people to understand what does - Necessary and Sufficient.

Next time someone uses that as a catch-phrase to shoot down a correlation as meaningless, ask them:
Does B require A? Necessary.
Does A lead to B? Sufficient.
QED, A causes B (or vice-versa).

Of course, my choice of the word "meaningless" there carries its own problems - Using correlation vs causation as a rhetorical shortcut to actual logic glosses over the fact that (statistically significant) correlations can have meaning (just that they don't "mean" causation). FWIW, The vast majority of modern medicine involves dealing with correlations rather than causes - "depressed people have low serotonin, prozac increases available serotonin", "people with high cholesterol have more heart attacks; lipitor reduces cholesterol". You can often use a correlation, as long as the two sides actually do link via some unknown variables. When they don't, however - Well, pirates don't prevent global warming because adding more pirates to the world doesn't somehow put us back before the industrial revolution.

Re:We need to make a new phrase popular (1)

Grizzley9 (1407005) | about 2 years ago | (#41530207)

and is becoming a quick way to short-circuit certain kinds of arguments The real problem here comes from people using that as a "short cut" to an actual argument. On the one hand, we've done a great job at getting them to grasp that correlation does not imply causation.

Emphasis mine. Correlation DOES suggest causation though as many here have already argued. It just doesn't prove/denote/equal it. Or to put it more in Slashdot terms correlation =/ causation. But it does imply, that's usually the basis of the first step in investigation.

Re:We need to make a new phrase popular (1)

Anonymous Coward | about 2 years ago | (#41530209)

One issue is that while "necessary and sufficient" may be sufficient for proving causation, it's not necessary to do so.

For example, decapitation (A) and death (B).
Does A lead to B? Yes.
Does B require A? No. A bullet through the heart will also lead to B.

Despite the fact that decapitation is not "necessary and sufficient" for death to occur, I don't think anyone would argue that decapitation doesn't cause death. Even "sufficient" is too strict for determining causation. Does the act of pulling a trigger on a gun cause a bullet to fire? Most would say yes. Is pulling a trigger *sufficient* to cause a bullet to fire? No. The bullet must be loaded, the firing pin must be present, etc., etc.

Don't get me wrong - "necessary and sufficient" is a great concept, and well worth having in your logical toolbox. I'm just not sure that it should be the gold standard in determining causation, though.

Re:We need to make a new phrase popular (1)

Beeftopia (1846720) | about 2 years ago | (#41530241)

Next time someone uses that as a catch-phrase to shoot down a correlation as meaningless, ask them:
Does B require A? Necessary.
Does A lead to B? Sufficient.
QED, A causes B (or vice-versa).

B is a flooded basement.
A is an overflowing washing machine.
N is a crack in the foundation allowing in water.

Multiple paths can lead to B. So, even if B doesn't require A, A can cause B. But N can cause B too.

Re:We need to make a new phrase popular (1)

Artifakt (700173) | about 2 years ago | (#41530303)

If we add enough pirates, and they are temporarily successful enough at stopping international trade, rading coastal settlements, and general rape and pillage, wouldn't putting civilization back before the industrial revolution, except in isolated pockets far inland, be a distinct possibility?

Dating advice (5, Insightful)

3ryon (415000) | about 2 years ago | (#41529961)

I had the phrase "Desired: A woman who understands that correlation does not imply causality..." in my dating profile.

I married the woman who replied. Yes, I am surprised that worked as well.

Re:Dating advice (2)

arth1 (260657) | about 2 years ago | (#41530229)

I go one step further, and require a basic understanding of Lorentz transformation.
And don't all of you girls here run down my mailbox, now...

Re:Dating advice (0)

Anonymous Coward | about 2 years ago | (#41530291)

I married the woman who replied.

Boy, that escalated quickly.

Re:Dating advice (0)

Anonymous Coward | about 2 years ago | (#41530295)

>Yes, I am surprised that worked as well.

Perhaps. Or maybe it was spurious.

Re:Dating advice (1)

Anonymous Coward | about 2 years ago | (#41530305)

Maybe it worked, maybe it didn't. Surely we can't assume that just because you had a statement about correlation/causation in your profile and you married the person who responded, that one caused the other.

Ah, one of my favorite pet peeves. (1)

Daniel Dvorkin (106857) | about 2 years ago | (#41530015)

TFA does a pretty good job of explaining why. Here's something I'd like to add: no, correlation does not imply causation, in the strict mathematical meaning of "imply"; in mathematical parlance, "A implies B" means that if A is true, B will always be true as well, and of course "X is positively correlated with Y" does not mean "an increase in X causes an increase in Y." But there's another meaning of "imply," and, like the common confusion about the meaning of the word "theory" in creationist arguments, it causes a lot of problems.

In common usage, "imply" carries a lot of ambiguity with it. In fact, it's almost never used to connote mathematical certainty. If you ask me, "Did John say he stole my money?" and I reply, "He implied that he did," that is a very different response from "Yes, that's what he said." In this usage, "A implies B" means that A is something which increases our estimate of the probability of B; if A is true, we're more likely to believe that B is true as well than if we had no information about A at all.

And in this sense, yes indeed, correlation does imply causation, and if you don't understand this then you should probably stop pretending that you understand the English language. Furthermore, it makes perfect mathematical sense. If you have data on both A and B, then if you can show a positive correlation, the hypothesis of a causal relationship will be much, much stronger than if you can't. And if you show a negative correlation, then forget about it. In other words, while "correlation implies causastion" isn't true in mathematical terms, the converse statement, "causation implies correlation," is true. Correlation is necessary though not sufficient for establishing causation.

Perhaps most importantly, every author of every peer-reviewed paper published in a respectable journal knows this. Next time you read some pop-sci reporting on any study in any field, and are tempted on that basis to dismiss it with "Correlation isn't causation, don't those dumb scientists know that?" ... stop. Think. Read the abstract. And if you want to discuss the results in any detail, read the paper, and understand the methodology. If it's paywalled, find a way to get access (I guarantee you that you can). And if you're unwilling to do this, then you should probably just keep quiet, because you do not know what you need to know to form an informed opinion.

BTW, the link in the summary goes to the second page of a two-page article. Here [slate.com] is a link to the single-page version.

Ugh... Yes, Correlation DOES Imply Causation (0)

Anonymous Coward | about 2 years ago | (#41530069)

Correlation does in fact imply causation, as any scientist who knows how to make use of their nose or their gut very early in the process of creating a hypothethis to test knows. It implies. It suggests. It's just that it may very well do so incorrectly. I've already given in to the fact that use of the phrase "correlation does not imply causation" instead of the phrase "correlation is not causation" will continue to annoy me and others who similarly like to at least try to get things right.

Hume (0)

Anonymous Coward | about 2 years ago | (#41530135)

shouldn't we thank David Hume for popularizing this idea?

How Is Babby Formed? (1)

Anonymous Coward | about 2 years ago | (#41530143)

How does gril get pregnat? It is obvious to even the most pedantic scientist that correlation always, always, always does in fact "imply" causation. Dr. Herbert West, your PhD should be revoked for making up an obnoxious and incorrect variant of the phrase "correlation does not equal causation."

Correlation does not imply causation (1)

Stirling Newberry (848268) | about 2 years ago | (#41530253)

But it gets the best odds in Vegas.

Correlation certainly implies causation (1)

gr8_phk (621180) | about 2 years ago | (#41530277)

We know fossil fuel use is on the rise. We know the earth is getting warmer. So you HAVE to see the FACT that people are using more fuel to run their air conditioners precisely BECAUSE it's hotter these days. Warming causes increased energy usage. duh.


That was a joke son, I'm not trolling....

antiscience (2)

PopeRatzo (965947) | about 2 years ago | (#41530281)

The most recent popularity of "correlation does not indicate causality" is the result of the rise of anti-intellecutalism and anti-reason. It's something that stupid people say to try to sound smart, and to deny data.

Correlation is not proof, but if you see replicable continual correlation, ignoring it is dumb.

It comes from people who try to use an 18th century view that Science "creates facts", instead of "creates models that either are supported by observation or are not supported by observation". Correlation is just another observation.

It's one of the big favorites of the anti-intellectual Right and climate change deniers.

Causation implies correlation (1)

Todd Knarr (15451) | about 2 years ago | (#41530351)

I always respond to that this way: "But causation does imply correlation. Since we can't directly see causes (if we could, we wouldn't be investigating looking for them) and we need something that we can see to tell us where to start looking, correlation is as good a starting point as we're going to get.".

While this phrase may date to 1880 or so... (1)

robkill (259732) | about 2 years ago | (#41530409)

The argument is "Cum Hoc Ergo Propter Hoc" as described in Latin. The similar phrase "Post Hoc, Ergo Propter Hoc" or "after this therefore because of this" dates back to 1704, according to Merriam Webster. I would assume "Cum Hoc Ergo Propter Hoc" is of similar age and origin.

"Post Hoc, Ergo Propter Hoc" (1)

srussia (884021) | about 2 years ago | (#41530855)

This is actually the most reasonable definition of "causation" for the following values:

"Hoc"= state of the Universe at a given instant

"Post Hoc"= state of the Universe at (given instant + infinitesimal interval)

Statistics can never prove causation (2)

Beeftopia (1846720) | about 2 years ago | (#41530503)

Statistics can ONLY show the degree of correlation. Statistics can never show causation. So, all you're ever going to get from statistics is correlation.

That reality escapes many.

References:
1) Although [statistical] regression cannot prove causation, no statistical method can do that, [harvardlawreview.org]

2) Epidemiological studies can never prove causation; that is, it cannot prove that a specific risk factor actually causes the disease being studied. Epidemiological evidence can only show that this risk factor is associated (correlated) with a higher incidence of disease in the population exposed to that risk factor. The higher the correlation the more certain the association, but it cannot prove the causation. [cornell.edu]

The reality is that statistics can ONLY show you whether there is a correlation or not, and how strong it is. Then it requires other methods to suggest whether there is a causative relationship.

Imply vs prove. (2)

Cyno01 (573917) | about 2 years ago | (#41530797)

I would argue that correlation absolutely IMPLIES causation, but does not PROVE causation.

Does correlation imply causation? (1)

TeknoHog (164938) | about 2 years ago | (#41530887)

No, but only because of Betteridge.
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