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.

A Generic EpiPen Coming in Early 2019 Could Save You Money

Brand-name EpiPens at a Congressional hearing on the escalating cost of the drug in 2016
Brand-name EpiPens at a Congressional hearing on the escalating cost of the drug in 2016
Alex Wong/Getty Images

For an incredibly common, life-saving medication, EpiPens (epinephrine auto-injectors) are surprisingly difficult for many consumers to get ahold of. Their cost has skyrocketed in recent years from less than $100 for a pack of two to more than $600. They’ve gotten so expensive that some EMTs have resorted to using syringes to manually administer epinephrine rather than purchasing the standard auto-injectors, which are almost exclusively made by the pharmaceutical company Mylan. Generic options have been slow to come to market, but according to Business Insider, a recently approved EpiPen rival is coming in the first few months of 2019, and it could save consumers a significant chunk of change.

The drug’s developers have had an unusually hard time getting the new EpiPen alternative, called Symjepi, onto store shelves. The drug was approved in 2017, but the company, Adamis Pharmaceuticals, had trouble finding investors. Now, Novartis, the Swiss-based pharmaceutical giant that manufactures drugs like Ritalin, is releasing the drug through its Sandoz division (perhaps most famous for it role in discovering LSD in the 1930s).

Symjepi will cost $250 out-of-pocket for a pack of two doses. That’s 16.6 percent less than the Mylan-authorized generic EpiPen or Teva’s generic EpiPen, which both sell for $300. It differs a bit from its rivals, though, in that it’s a pre-filled, single-dose syringe rather than a spring-loaded auto-injector. Auto-injectors are plastic, pen-like devices that keep the needle shielded until the moment of injection, and are specifically designed to help make it easier for untrained (even squeamish) people to use in an emergency. With this version, patients will need to remove a needle cap and inject the needle. Just like the EpiPen, though, it’s designed to be injected in the upper thigh, through clothing if necessary.

If you have health insurance, the difference in cost may not matter as much for you as a consumer, depending on your plan. (I personally picked up a two-pack of Mylan-authorized generic Epipens at CVS recently for $0, using a manufacturer’s Epipen coupon to knock down what would have been a $10 copay.) But it will matter considerably for those with high-deductible plans and to insurers, which, when faced with high costs, eventually pass those costs on to the consumer either through higher co-pays or higher premiums. It also affects agencies that buy EpiPens for emergency use, like local fire departments. And since EpiPens expire after just a year, the costs add up.

However, there’s currently a shortage of EpiPens on the market, according to the FDA, making it more important than ever to have other epinephrine drugs available to those at risk for serious allergic reactions.

[h/t Business Insider]

Brain-Eating Amoeba Kills Seattle Woman Who Used Tap Water in Her Neti Pot

CDC/Dr. Govinda S. Visvesvara, Wikimedia Commons // Public domain
CDC/Dr. Govinda S. Visvesvara, Wikimedia Commons // Public domain

If you use a neti pot to clear out your sinuses, there's one important rule you should always follow: Don't fill it with tap water. Doing so could land you a sinus infection, or worse, a potentially fatal disease caused by a brain-eating amoeba. Although the latter scenario is exceptionally rare, a 69-year-old woman in Seattle died from doing just that, The Seattle Times reports. Experts are also warning that these infections could become more common as temperatures in the northern hemisphere continue to rise.

Physicians at Seattle's Swedish Medical Center initially thought the woman had a brain tumor. She was brought into the emergency room following a seizure, and a CT scan of her brain seemed to reveal a tumor-like mass. The only other known symptom she had was a red sore on her nose, which was previously misdiagnosed as rosacea. When surgeons operated on her the following day, they noticed that "a section of her brain about the size of a golf ball was bloody mush," neurosurgeon Dr. Charles Cobbs told The Seattle Times. "There were these amoeba[e] all over the place just eating brain cells. We didn't have any clue what was going on, but when we got the actual tissue we could see it was the amoeba."

She died a month later of an infection called granulomatous amoebic encephalitis (GAE), according to a recent case report published in the International Journal of Infectious Diseases. The disease is caused by a single-celled amoeba called Balamuthia mandrillaris, and it's extremely deadly. Of the 109 cases between 1974 and 2016, 90 percent were fatal.

According to the FDA, some bacteria and amoebae in tap water are safe to swallow because acid in the stomach kills them. However, when they enter the nasal cavity, they can stay alive for long periods of time and travel up to the brain, where they start eating their way through tissue and cells. Another brain-eating amoeba called Naegleria fowleri can cause a similar disease, except it acts faster and can cause death in just a few days. Although it's also rare, it's usually found in warm freshwater, and infections start by getting contaminated water up one's nose while swimming or by using a nose irrigation device filled with tap water.

Dr. Cynthia Maree, an infectious disease doctor at the Swedish Medical Center, said the changing environment could facilitate the spread of these infections. "I think we are going to see a lot more infections that we see south (move) north, as we have a warming of our environment," Maree says. Researchers say these amoebae are still little-understood. Future studies would need to be conducted to learn more about the risk factors involved.

[h/t The Seattle Times]