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.

1. EAT ENOUGH CHOCOLATE AND YOU'LL WIN A NOBEL.

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.

2. THE NIGHT-LIGHT BIZ IS IN CAHOOTS WITH YOUR OPTHALMOLOGIST.

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.

3. BLACK CATS ARE SO UNLUCKY, THEY'LL GIVE YOU ALLERGIES.

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.

4. FORGET ABOUT APPLES: HEAD LICE KEEPS THE DOCTOR AWAY.

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.

5. SERVING BREAKFAST WILL BOOST YOUR CHILD'S REPORT CARD.

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.

6. STORKS AND BABIES ARE INEXTRICABLY INTERTWINED.

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.”

7. IF YOU'RE A DIEHARD FAN, LOSING THE SUPER BOWL WILL LITERALLY KILL YOU.

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.

8. EMPLOYED? THANK YOUR OVERPRICED GROCERY STORE.

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.

9. LONELY PEOPLE KEEP THE SPA INDUSTRY ROLLING IN THE DOUGH.

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.

10. THE POPE SHOULD PRAY FOR THE WELSH RUGBY TEAM... TO LOSE.

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.

Fossilized Fat Shows 550-Million-Year-Old Sea Creature May Have Been the World's First Animal

Ilya Bobrovskiy, the Australian National University
Ilya Bobrovskiy, the Australian National University

A bizarre sea creature whose fossils look like a cross between a leaf and a fingerprint may be Earth's oldest known animal, dating back 558 million years.

As New Scientist reports, researchers from the Australian National University (ANU) made a fortunate find in a remote region of Russia: a Dickinsonia fossil with fat molecules still attached. These odd, oval-shaped creatures were soft-bodied, had rib structures running down their sides, and grew about 4.5 feet long. They were as “strange as life on another planet,” researchers wrote in the abstract of a new paper published in the journal Science.

Another variety of fossil
Ilya Bobrovskiy, the Australian National University

Although Dickinsonia fossils were first discovered in South Australia in 1946, researchers lacked the organic matter needed to classify this creature. "Scientists have been fighting for more than 75 years over what Dickinsonia and other bizarre fossils of the Edicaran biota were: giant single-celled amoeba, lichen, failed experiments of evolution, or the earliest animals on Earth,” senior author Jochen Brocks, an associate professor at ANU, said in a statement.

With the discovery of cholesterol molecules—which are found in almost all animals, but not in other organisms like bacteria and amoebas—scientists can say that Dickinsonia were animals. The creatures swam the seas during the Ediacaran Period, 635 million to 542 million years ago. More complex organisms like mollusks, worms, and sponges didn’t emerge until 20 million years later.

The fossil with fat molecules was found on cliffs near the White Sea in an area of northwest Russia that was so remote that researchers had to take a helicopter to get there. Collecting the samples was a death-defying feat, too.

“I had to hang over the edge of a cliff on ropes and dig out huge blocks of sandstone, throw them down, wash the sandstone, and repeat this process until I found the fossils I was after,” lead author Ilya Bobrovskiy of ANU said. Considering that this find could change our understanding of Earth’s earliest life forms, it seems the risk was worth it.

[h/t New Scientist]

The Weird, Disturbing World of Snail Sex

iStock
iStock

Romance is rare in the animal kingdom. Instead of wooing their partners before copulating, male ducks force themselves onto females, depositing genetic material with spiky, corkscrew penises. Then, there's tardigrade sex, which is less violent but not exactly heartwarming. Females lay eggs into a husk of dead skin. The male then ejaculates onto the eggs while stroking the female, and the whole process can take up to an hour.

But you can't talk about disturbing mating rituals in nature without mentioning snails. If you're unfamiliar with snail sexuality, you may assume that snail sex falls on the vanilla side: The mollusks, after all, are famous for being slow-moving and they don't even have limbs. But if you have the patience to watch a pair of snails going at it, you'll notice that things get interesting.

The first factor that complicates snail sex is their genitalia. Snails are hermaphrodites, meaning individuals have both a male set and female set of parts, and any two snails can reproduce with each other regardless of sex. But in order for a couple of snails to make little snail babies, one of them needs to take on the role of the female. That's where the love dart comes in.

The love dart, technically called a gypsobelum, isn't exactly the Cupid's arrow the name suggests. It's a nail-clipping-sized spike that snails jab into their partners about 30 minutes before the actual sex act takes place. The sliver is packed with hormones that prepare the receiving snail's body for sperm. Depending on the species, only one snail might release the dart, or they both might in an attempt to avoid becoming the female of the pair. You can watch the action in the video below.

For sex to be successful, both snails must insert their penises into the other's vaginal tracts at the same time. Both snails deposit sperm, and the strength of the love dart ultimately determines whether or not that sperm fertilizes their partner's eggs.

That's assuming the snail survives the little love-stab. In human proportions, the love dart is the equivalent of a 15-inch knife. Fortunately, snails are resilient creatures, and gastropod researcher Joris Koene tells KQED he's only ever seen one snail die from the transfer.

Snails also have a way of making it up to their partners after skewering them with a hormone stick. Their sperm deposit contains a dose of fortifying nutrients, something scientists refer to as a nuptial gift. It may not equal the energy expended during sex, but its enough to give them a small post-coital boost.

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