10 Times Correlation Was Not Causation

Katie Carey
Katie Carey

It’s a scientist’s mantra: Correlation does not imply causation. But sometimes wrong feels so right.


If you want to boost blood flow to your brain and (potentially) slow cognitive decay, consume flavanols. The plant compounds, found in green tea and cocoa, are great for getting blood into your noggin. That made New York doctor Franz Messerli wonder: Would a nation of bonbon–eaters be more intellectually accomplished than a country that didn’t consume as much cocoa? In a tongue-in-cheek 2012 paper published in The New England Journal of Medicine, he found that countries that ate a lot of chocolate also won the most Nobel Prizes. Messerli published the study with a wink, but some media outlets took the news seriously, failing to see that a confounding variable was at play—wealth. A richer country (like Switzerland, which has 26 Nobel winners) will have more quality scientific research—and well-stocked shelves of chocolate, too.


Nearsightedness has been increasing worldwide for decades. In some Asian countries, up to 90 percent of adults can’t see distant objects clearly, and in 1999, researchers at the Children’s Hospital of Philadelphia thought they’d found the cause: night-lights. The evidence suggested that kids who slept with a light developed myopia later in life. But two groups of researchers argued that the study failed to see the evidence in front of its nose—myopic parents have myopic kids. And myopic parents, who can’t see well in the dark, are more likely to install night-lights in their children’s rooms.


Are black cats bad luck for your sinuses? In a January 2000 paper for the Journal of Allergy and Clinical Immunology, researchers found that people with dark-colored cats suffered more allergic reactions than owners of light-colored cats (or no kitty at all). But the correlation appears to have just been a coincidence. Cat allergies are actually caused by a protein called Fel d 1, which is produced in salivary and sebaceous glands. A research team in New Zealand found that cat allergies simply aren’t related to cat color or hair length.


For centuries, natives of the New Hebrides islands considered a head full of lice a sign of good health. “Observation over the centuries had taught them that people in good health usually had lice and sick people very often did not. The observation itself was accurate and sound,” writes Darrell Huff in How to Lie with Statistics. But the correlation didn’t mean lice are the key to good health—it’s the other way around. Healthy people had lice because their body was just the right temperature, a perfect home for bugs. But when people ran a high fever, their flesh became hot, sending the lice scattering. Lice didn’t cause good health—they preyed on it.


We’ve all heard that kids who eat breakfast do better in school. It makes sense; it’s hard to focus on an empty stomach. But despite their best attempts, researchers haven’t been able to pinpoint why breakfast aids learning—if that’s even the case. A 1996 study of Jamaican students found that, in some schools, kids behaved better after they ate breakfast; in other schools, they acted worse. The gap probably had more to do with each school’s resources than with a student’s daily ration of Cocoa Puffs. Students at well-equipped schools behave better regardless of their diet.


Storks do not deliver babies. That bit of German folklore likely originated because the white stork’s migration rituals last nine months. (Plus, Hans Christian Andersen helped popularize the myth in his short story “The Storks.”) But that hasn’t stopped scientists from acknowledging a striking correlation: Between 1970 and 1985, the number of breeding pairs of white storks in Lower Saxony dropped. Over the same period, the birth rate there also fell. Meanwhile, stork numbers increased in Berlin’s suburbs, where doctors delivered more babies. As Robert Matthews writes in Teaching Statistics, “While storks may not deliver babies, unthinking interpretation of correlation ... can certainly deliver unreliable conclusions.”


Hours after the Seattle Seahawks lost the Super Bowl in 2015, fan Michael Sven Vedvik died. In his obituary, his family blamed the team’s “lousy play call for Mike’s untimely demise.” The joke echoed 2011 research in Clinical Cardiology linking Super Bowl losses to a 15 to 27 percent increase in cardiac deaths in the loser’s hometown. (The Grim Reaper has tried wearing cleats at least once: When the Steelers’ Jerome Bettis fumbled in a 2006 playoff game, a fan watching from a bar became so upset that he had a heart attack. Fortunately, he survived.) Problem is, the studies don’t take non-football variables into account. And the data in one study investigated deaths that occurred two weeks after the game. “I don’t think that everyone who dies within 14 days of the Super Bowl died because of the Super Bowl,” David Prince of Albert Einstein College of Medicine told Live Science.


In 1958, economist William Phillips published a paper claiming that when unemployment increased, inflation decreased (and vice versa). “That led nations to start thinking of these two variables as trade-offs,” says Rebecca Goldin, professor of math at George Mason University and director of the website Sense About Statistics. “Some would focus on unemployment while others focused on controlling inflation, but they all saw this as a causal trade-off.” Then came the 1970s, when many countries saw both high inflation and high unemployment. Turns out Phillips’s “rule” was just a short-term coincidence. While inflation can affect unemployment for short periods, it can’t fix joblessness over the long run.


In Scandinavia, people fight the cold of winter with cozy candlelit social gatherings. Called hygge in Denmark and koselig in Norway, the tradition suggests there’s a connection between physical temperature and the “social warmth” of friends. In 2011, Yale researchers suggested that people may instinctively reach for that connection in the shower. In a study, they found that lonely people were more likely to take long, warm showers and baths. Was it because higher temperatures make them feel less isolated? Well, the methodology left critics cold. The study used a small sample (only 51 undergrads); of those, 90 percent reported bathing or showering less than once a week. Not exactly a trusty sample. In 2014, a different team tried to replicate the results using a larger (and presumably better-smelling) group, and failed.


According to the 2008 study “Rugby (the Religion of Wales) and its Influence on the Catholic Church,” the Pope is more likely to die when the Welsh rugby team wins the sport’s Grand Slam. The paper—which appeared in the British Medical Journal’s humorous annual Christmas issue—found no connection between the pontiff’s mortality and teams from other countries. Just Wales. We expect a Dan Brown book about this any time now.

Here’s What You Need to Know About the New Coronavirus

jarun011/iStock via Getty Images
jarun011/iStock via Getty Images

This article has been updated.

This morning, the Centers for Disease Control and Prevention (CDC) confirmed the fifth case of the recently discovered coronavirus in the U.S. Find out what it is, where it is, how to avoid it, and all the other need-to-know information about the illness below.

What is the new coronavirus?

Coronaviruses are a group of viruses named for the crown-shaped spikes that cover their surfaces (corona is the Latin word for crown). According to the CDC, human coronaviruses can cause upper-respiratory tract illnesses, including the common cold, and can sometimes lead to more severe lower-respiratory tract issues like pneumonia or bronchitis.

Because this latest coronavirus, 2019-nCoV, is so new, health officials are currently trying to figure out how it works and how to treat it. It’s not the first time a potent new coronavirus has caused an international outbreak: SARS-CoV originated in Asia and spread to more than two dozen countries in 2003, and MERS-CoV first infected people in Saudi Arabia before spreading across the globe in 2012.

Where is the coronavirus outbreak happening?

Overall, China has more than 2700 confirmed cases, many of which are in Wuhan, a city in China’s Hubei province where 2019-nCoV was first detected last month. Around 50 additional cases have been reported in South Korea, Japan, Singapore, Hong Kong, Macao, Taiwan, Thailand, and Vietnam.

The CDC has confirmed five U.S. cases—in California, Arizona, Illinois, and Washington—all of whom had recently returned from trips to Wuhan. Right now, the CDC is screening all passengers from Wuhan, and their flights are only allowed to land at one of five U.S. airports: John F. Kennedy International Airport in New York, Los Angeles International Airport, San Francisco International Airport, Hartsfield-Jackson Atlanta International Airport, or Chicago O’Hare International Airport.

Chinese officials have shut down transportation to and from Wuhan, and they’re also temporarily closing tourist spots like Beijing’s Forbidden City, Shanghai Disneyland, and a portion of the Great Wall.

What are the symptoms of the new coronavirus?

Symptoms are similar to those caused by a cold or the flu, including fever, dry cough, and breathing difficulty. As of Monday morning, 81 people in China had died from the virus, and The New York Times reported that older people with preexisting conditions like cirrhosis, diabetes, and Parkinson’s disease are most likely to be affected.

How does the new coronavirus spread?

Because most of the early cases of 2019-nCoV were traced back to a seafood and meat market in Wuhan, health officials think the virus originally spread from infected animals to humans, but it’s now being transmitted from person to person.

Though scientists are still studying exactly how that happens, the leading theory is that it travels in tiny droplets of fluid from the respiratory tract when a person coughs or sneezes.

How do you avoid the new coronavirus?

The CDC is warning everyone to avoid any nonessential trips to Wuhan, and to avoid animals or sick people if you’re traveling elsewhere in China. If you’ve been to China in the last two weeks and experience any of the symptoms listed above, you should seek medical attention immediately—and you should call the doctor’s office or emergency room beforehand to let them know you’re coming.

Otherwise, simply stick to the precautions you’d normally take when trying to stay healthy: Wash your hands often with soap and water, cover your nose and mouth when coughing or sneezing, stay away from sick people, and thoroughly cook any meat or eggs before eating them.

Should you be worried about the new coronavirus?

The global health community is taking 2019-nCoV seriously in order to curb the outbreak as quickly as possible, but you definitely shouldn’t panic. The CDC maintains that it’s a low-risk situation in the U.S., and public health officials are echoing that message.

Caitlin Wolfe, a former consultant epidemiologist for the World Health Organization (WHO) and current doctoral student at the University of South Florida’s College of Public Health, tells Mental Floss that it’s too early to tell if the virus will become a nationwide outbreak, but the fact that cases have been detected in the U.S. “means patients and physicians are paying attention to the relevant symptoms and travel history,” and “the public health systems we have here are working.”

“The most important messages to get out to the American public are ones that share the information we know and avoid the alarmist/sensationalist narrative,” Wolfe says. “Early estimates from the Chinese authorities suggest that the R0, or the average number of people each person with the virus infects, is between 1.4 and 2.5. To put this in perspective, the average number of susceptible people infected by someone with the measles virus is between 12 and 18.”

While experts work to understand and fight the virus, keep an eye out for updates from the CDC and WHO and be extra committed to practicing good hygiene habits—which, as Wolfe points out, will also help protect you from the flu or even just a regular cold.

[h/t USA Today]

Has An Element Ever Been Removed From the Periodic Table?

lucadp/iStock via Getty Images
lucadp/iStock via Getty Images

Barry Gehm:

Yes, didymium, or Di. It was discovered by Carl Mosander in 1841, and he named it didymium from the Greek word didymos, meaning twin, because it was almost identical to lanthanum in its properties. In 1879, a French chemist showed that Mosander’s didymium contained samarium as well as an unknown element. In 1885, Carl von Weisbach showed that the unknown element was actually two elements, which he isolated and named praseodidymium and neodidymium (although the di syllable was soon dropped). Ironically, the twin turned out to be twins.

The term didymium filter is still used to refer to welding glasses colored with a mixture of neodymium and praseodymium oxides.

One might cite as other examples various claims to have created/discovered synthetic elements. Probably the best example of this would be masurium (element 43), which a team of German chemists claimed to have discovered in columbium (now known as niobium) ore in 1925. The claim was controversial and other workers could not replicate it, but some literature from the period does list it among the elements.

In 1936, Emilio Segrè and Carlo Perrier isolated element 43 from molybdenum foil that had been used in a cyclotron; they named it technetium. Even the longest-lived isotopes of technetium have a short half-life by geological standards (millions of years) and it has only ever been found naturally in minute traces as a product of spontaneous uranium fission. For this reason, the original claim of discovery (as masurium) is almost universally regarded as erroneous.

As far as I know, in none of these cases with synthetic elements has anyone actually produced a quantity of the element that one could see and weigh that later turned out not to be an element, in contrast to the case with didymium. (In the case of masurium, for instance, the only evidence of its existence was a faint x-ray signal at a specific wavelength.)

This post originally appeared on Quora. Click here to view.