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Why eating ice cream is linked to shark attacks
Why are soda and ice cream each linked to violence? This article delivers the final word on what people mean by "correlation does not imply causation."
- Ice cream consumption is actually linked to shark attacks.
- But the relationship is correlative, not causal.
- It's pretty stunning how media outlets skip over this important detail.
Soda and ice cream are linked to violence. What the what? And people have concluded from data that smoking, chocolate, and curly fries are good for you. Why the when?
I'll explain -- but also go much further and show you… wait for it… that figuring out why such things are true doesn't even matter at all for driving decisions with data. Who the how? It's time for the "correlation does not imply causation" clarification proclamation moment of zen clarity. Let's do this!
Ice cream and shark attacks
Ice cream cone and a shark.
According to the data, ice cream consumption is linked to shark attacks. How the why? Well, maybe eating ice cream makes you taste better? So, you consume the ice cream and the shark consumes you. But the more accepted sharksplanation is that it's seasonal. It just so happens that, when it's warmer, more people are eating ice cream and also more people are swimming in the ocean.
That is to say that there's no causal relationship, in either direction -- neither of these things causes the other, even indirectly. Instead, they're both caused by a third factor. So the good news is that we've found a link, a connection, a correlation between these two factors in the data -- and that's valuable. The two are indeed predictive of one another. If we see ice cream sales increase, we can rightly ascertain a higher probability of shark attacks, and vice versa. But the bad news is that, when we discover such a correlation, oftentimes their common cause, some third factor, is just not in our data set at all. That data wasn't included, 'cause it was overlooked or perhaps it would be difficult or costly to collect. So we're stuck with a predictive correlation, but no definitive causal explanation as to why it is so.
Soda and violence
This headline about soda turning teens into killers is really something.
Now, soda also appears to be dangerous. In 2011, an economics professor and a health policy researcher went public with this as their research result. Among adolescents, they found, "a strong association between soft drinks and violence..." And they also wrote, "... drinking more than five cans of non-diet soft drinks per week was associated with a 9–15 percentage point increase in the probability of engaging in violent actions... There may be a direct cause-and-effect relationship, perhaps due to the sugar or caffeine content of soft drinks."Well, after that, a cacophony of media coverage erupted, with headlines like, "Soda Totally Turns Teens Into Killers." Then skeptics began to push back. Now, they didn't question the correlation between soda consumption and violence. Rather, they questioned the causal relationship. Ya see, you can conclude that there's a link, a connection, an association, a correlation between two factors without necessarily understanding why it is so. The "why" -- the explanation -- always involves causation: some insight as to how things influence or affect one another.
The criticism here is that you shouldn't conclude soda causes violence. Rather, it may be that diet is linked to socio-economic status. Lower income teens consume more junk food, including sodas, and poverty itself is a risk factor for teen violence. Now if that story is true, the causal links shown here -- like, the exact way in which poverty leads to violence -- could be pretty complex and somewhat multi-staged, but the point is that this is a plausible alternative explanation that doesn't have soda even indirectly causing violence, so it's unwarranted to sound the alarm about the dangers of soda.
Let me put it another way. Even if it's true that violent people drink more soda, there's no reason to fully believe that drinking soda will make you more violent. That would be like assuming that eating more ice cream will cause more shark attacks. Ice cream and soda may be bad for you, but not in that way.
Chocolate eaters are more slim
The operative word here is 'may'. Also, 'may not' would equally apply.
Anyway, now some great news: Some tempting vices are good for you, like chocolate, smoking, curly fries, and breakfast! ...is what people who presume causation say.
"More frequent chocolate intake is linked to a lower body mass index," according to three University of California medical and economics researchers who published this finding. Their writing states that this association "could be causal," since chocolate might lessen the depositing of fat.
And cue the media frenzy. A BBC headline announced, "Chocolate 'May Help Keep People Slim,'" and a Wall Street Journal video with "It appears to make you thin" in its caption kicks off with, "It doesn't make you fatter."
Now, I would say that people's passionate love for chocolate precipitates this wishful thinking and bold presumption of causation... but then again I can't really be sure what caused them to fudge it. It's funny 'cause it's true.
Correlation does not imply causation
Anyway, the discovery of a correlation between two items does not mean one causes the other, not even indirectly. It just doesn't necessarily tell us anything about any causal relationship. The hallways of universities and the chatrooms of the Internet echo with a frequent reminder of this utmost, dire warning:
"Correlation does not imply causation."
Statisticians absolutely scream this rule from the rooftops just as often as the popular press and big data hacks overlook it.
Now, looking at chocolate consumption and a lower body mass index, another plausible causal explanation would be that people reward themselves with chocolate when they lose weight. That is, lower weight leads to chocolate consumption, rather than the other way around.
Or, it could be that people just eat more chocolate because they weren't trying to lose weight in the first place because they were already thin.
Or another possibility is that poverty, which has been tied to higher weight, also makes chocolate less affordable, so people with a lower income weigh more on average and yet also eat less chocolate.
Or it could be some combination of all these different causal relationships. We don't know. The main point is, you gotta live in that uncertainty and avoid the temptation to presume a specific causal relationship when only correlation has been established. Adjust your brain to accept this lack of knowledge.
Smokers suffer less repetitive motion disorder
A seal smoking a pipe.
Another example: Smokers suffer less from repetitive motion disorder. An ergonomics consultant found that, among editors at a major metropolitan newspaper, those who smoked cigarettes were less likely to develop carpal tunnel syndrome. Could it be that this is a veritable health benefit of smoking? I don't think so! The consultant believes it was because smokers take more breaks.
That does seem like a more likely explanation to me, but remember that the correlation in the data in and of itself provides no evidence that one explanation is more likely than another. Scientifically establishing causation usually requires collecting data by way of an experimental setup that includes having a control group. But most of the data out there wasn't collected for science. Typical "big data" projects leverage the tremendous load of data that companies generate in the normal course of conducting business. Today's priceless explosion of data exists only as a fortunate side effect. Such data, also known as "found data," is like data from a typical survey or so-called "longitudinal" research in that it doesn't include any purposefully held-aside control group. So typical "big data" serves to establish correlations but not causation.
Curly fries and breakfast
These curly fries are looking delicious.
Guess what else. People who like "Curly Fries" on Facebook are more intelligent. So does that mean eating curly fries makes you smarter? Well, that would throw you for a loop. Instead, researchers believe it was just that a Facebook page for this fun food item happened to gain popularity among a group of relatively smart people.
And finally, men who eat breakfast face a lower risk of coronary heart disease. However, that doesn't necessarily mean breakfast deserves its reputation as the most important meal of the day. We can't conclude this connection results from the food itself being good for you. Instead, the researchers suggest that eating breakfast is a proxy for lifestyle -- if you're leading a busy, high-stressed life, you're more likely to skip breakfast and you're also subjected to a higher health risk. But, once again, that's largely just an intuitive hunch. As always, there are other plausible explanations.
Causality is only an avocational interest
Now, you may be asking, doesn't Dr. Data even care why these things are true? Isn't he at least curious? Well, yeah, for sure -- but it isn't my day job. People in the "real sciences" like physics, chemistry, and medical research have their work cut out for them. They have to figure out how the world works, why things happen the way they do. I don't envy them — 'cause we data scientists have it much easier. Most deployments of machine learning improve decision-making without scientifically investigating causal effects.
In fact, this point was once put quite bluntly by a chief analytics officer of the New York City mayor's office in a published interview — and this is a real: "Causation is for other people... it is very dicey... You know, we have real problems to solve. I can't dick around, frankly, thinking about other things like causation right now."
Ok, message received!
So, if a higher risk level is predicted for an individual, we don't necessarily need to understand why in order to take precautions accordingly. For example, screening men who skip breakfast for heart disease could be useful, even if we don't necessarily believe scrambled eggs and cornflakes are what make the difference to your health.
About the Dr. Data show
This article is based on a transcript from The Dr. Data Show.
This new web series breaks the mold for data science infotainment, captivating the planet with short webisodes that cover the very best of machine learning and predictive analytics. Click here to view more episodes and to sign up for future episodes of The Dr. Data Show.
- Correlation vs causation: The limitations of deep learning - Big Think ›
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- Googling medical symptoms likely 'OK', study finds - Big Think ›
"Deepfakes" and "cheap fakes" are becoming strikingly convincing — even ones generated on freely available apps.
- A writer named Magdalene Visaggio recently used FaceApp and Airbrush to generate convincing portraits of early U.S. presidents.
- "Deepfake" technology has improved drastically in recent years, and some countries are already experiencing how it can weaponized for political purposes.
- It's currently unknown whether it'll be possible to develop technology that can quickly and accurately determine whether a given video is real or fake.
After former U.S. President William Henry Harrison delivered his inaugural speech on March 4, 1841, he posed for a daguerreotype, the first widely available photographic technology. It became the first photo taken of a sitting American president.
As for the eight presidents before Harrison, history can see them only through artistic renderings. (The exception is a handful of surviving daguerreotypes of John Quincy Adams, taken after he left office. In his diary, Adams described them as "hideous" and "too true to the original.")
But a recent project offers a glimpse of what early presidents might've looked like if photographed through modern cameras. Using FaceApp and Airbrush, Magdalene Visaggio, author of books such as "Eternity Girl" and "Kim & Kim," generated a collection of convincing portraits of the nation's first presidents, from George Washington to Ulysses S. Grant.
Modern Presidents George Washington https://t.co/CURJQB0kap— Magdalene Visaggio (@Magdalene Visaggio)1611952243.0
What might be surprising is that Visaggio was able to generate the images without a background in graphic design, using freely available tools. She wrote on Twitter:
"A lot of people think I'm a digital artist or whatever, so let me clarify how I work. Everything you see here is done in Faceapp+Airbrush on my phone. On the outside, each takes between 15-30 mins. Washington was a pretty simple one-and-done replacement."
Ulysses S Grant https://t.co/L1IGXLI3Vl— Magdalene Visaggio (@Magdalene Visaggio)1611959480.0
"Other than that? I am not a visual artist in any sense, just a hobbyist using AI tools see what she can make. I'm actually a professional comics writer."
Did another pass at Lincoln. https://t.co/PdT4QVpMbn— Magdalene Visaggio (@Magdalene Visaggio)1611973947.0
Of course, Visaggio isn't the first person to create deepfakes (or "cheap fakes") of politicians.
In 2017, many people got their first glimpse of the technology through a video depicting former President Barack Obama warning: "We're entering an era in which our enemies can make it look like anyone is saying anything at any point in time." The video quickly reveals itself to be fake, with comedian Jordan Peele speaking for the computer-generated Obama.
While deepfakes haven't yet caused significant chaos in the U.S., incidents in other nations may offer clues of what's to come.
The future of deepfakes
In 2018, Gabon's president Ali Bongo had been out of the country for months receiving medical treatment. After Bongo hadn't been seen in public for months, rumors began swirling about his condition. Some suggested Bongo might even be dead. In response, Bongo's administration released a video that seemed to show the president addressing the nation.
But the video is strange, appearing choppy and blurry in parts. After political opponents declared the video to be a deepfake, Gabon's military attempted an unsuccessful coup. What's striking about the story is that, to this day, experts in the field of deepfakes can't conclusively verify whether the video was real.
The uncertainty and confusion generated by deepfakes poses a "global problem," according to a 2020 report from The Brookings Institution. In 2018, the U.S. Department of Defense released some of the first tools able to successfully detect deepfake videos. The problem, however, is that deepfake technology keeps improving, meaning forensic approaches may forever be one step behind the most sophisticated forms of deepfakes.
As the 2020 report noted, even if the private sector or governments create technology to identify deepfakes, they will:
"...operate more slowly than the generation of these fakes, allowing false representations to dominate the media landscape for days or even weeks. "A lie can go halfway around the world before the truth can get its shoes on," warns David Doermann, the director of the Artificial Intelligence Institute at the University of Buffalo. And if defensive methods yield results short of certainty, as many will, technology companies will be hesitant to label the likely misrepresentations as fakes."
Ancient corridors below the French capital have served as its ossuary, playground, brewery, and perhaps soon, air conditioning.
- People have been digging up limestone and gypsum from below Paris since Roman times.
- They left behind a vast network of corridors and galleries, since reused for many purposes — most famously, the Catacombs.
- Soon, the ancient labyrinth may find a new lease of life, providing a sustainable form of air conditioning.
Ancient mining areas below Paris for limestone (red) and gypsum (green).Credit: Émile Gérards (1859–1920) / Public domain
"If you're brave enough to try, you might be able to catch a train from UnLondon to Parisn't, or No York, or Helsunki, or Lost Angeles, or Sans Francisco, or Hong Gone, or Romeless."
China Miéville's fantasy novel Un Lun Dun is set in an eerie mirror version of London. In it, he hints that other cities have similar doubles. On the list that he offhandedly rattles off, Paris stands out. Because the City of Light really does have a twisted sister. Below Paris Overground is Paris Underground, the City of Darkness.
Most people will have heard of the Catacombs of Paris: subterranean charnel houses for the bones of around six million dead Parisians. They are one of the French capital's most famous tourist attractions – and undoubtedly its grisliest.
But they constitute only a small fragment of what the locals themselves call les carrières de Paris ("the mines of Paris"), a collection of tunnels and galleries up to 300 km (185 miles) long, most of which are off-limits to the public, yet eagerly explored by so-called cataphiles.
The Grand Réseau Sud ("Great Southern Network") takes up around 200 km beneath the 5th, 6th, 14th, and 15th arrondissements (administrative districts), all south of the river Seine. Smaller networks run beneath the 12th, 13th, and 16th arrondissements. How did they get there?
Paris stone and plaster of Paris
It all starts with geology. Sediments left behind by ancient seas created large deposits of limestone in the south of the city, mostly south of the Seine; and gypsum in the north, particularly in the hills of Montmartre and Ménilmontant. Highly sought after as building materials, both have been mined since Roman times.
The limestone is also known as Lutetian limestone (Lutetia is the Latin name for ancient Paris) or simply "Paris stone." It has been used for many famous Paris landmarks, including the Louvre and the grand buildings erected during Georges-Eugène Haussmann's large-scale remodelling of the city in the mid-19th century. The stone's warm, yellowish color provides visual unity and a bright elegance to the city.
The fine-powdered gypsum of northern Paris, used for making quick-setting plaster, was so famed for its quality that "plaster of Paris" is still used as a term of distinction. However, as gypsum is very soluble in water, the underground cavities left by its extraction were extremely vulnerable to collapse.
Like living on top of a rotting tooth: subsidence starts far below the surface, but it can destroy your house.Credit : Delavanne Avocats
In previous centuries, a road would occasionally open up to swallow a chariot, or even a whole house would disappear down a sinkhole. In 1778, a catastrophic subsidence in Ménilmontant killed seven. That's why the Montmartre gypsum quarries were dynamited rather than just left as they were. The remaining gypsum caves were to be filled up with concrete.
The official body governing Paris down below is the Inspection Générale des Carrières (IGC), founded in the late 1770s by King Louis XVI. The IGC was tasked with mapping and, where needed, propping up the current and ancient (and sometimes forgotten) mining corridors and galleries hiding beneath Paris.
A delightful hiding place
Also around that time, the dead of Paris were getting in the way of the living. At the end of the 18th century, their final destination consisted of about 200 small cemeteries, scattered throughout the city — all bursting at the seams, so to speak. There was no room to bury the newly dead, and the previously departed were fouling up both the water and air around their respective churchyards.
Something radical had to happen. And it did. From 1785 until 1814, the smaller cemeteries were emptied of their bones, which were transported with full funerary pomp to their final resting place in the ancient limestone quarries at Tombe-Issoire. Three large and modern cemeteries were opened to receive the remains of subsequent generations of Parisians: Montparnasse, Père-Lachaise, and Passy.
The six million dead Parisians in the Catacombs, from all corners of the capital and across many centuries, together form the world's largest necropolis — their now anonymized skulls and bones methodically stacked, occasionally into whimsical patterns. The Catacombs are fashioned into a memorial to the brevity of life. The message above the entrance reads: Arrête! C'est ici l'empire de la Mort. ("Halt! This is the empire of Death.")
That has not stopped the Catacombs, accessible via a side door to a classicist building on the Avenue du Colonel Henri Rol-Tanguy, making just about every Top 20 list of things to see in Paris.
An underground economy
However, while the Catacombs certainly are the most famous part of the centuries-old network beneath Paris, and in non-pandemic times draw thousands of tourists each day, they constitute just 1.7 km (1 mile) of the 300-km (185-mile) tunneling total.
Subterranean Paris wasn't just used for mining and storing dead people. In the 17th century, Carthusian monks converted the ancient quarries under their monastery into distilleries for the green or yellow liqueur that still carries their name, chartreuse.
Because the mines generally keep a constant cool temperature of around 15° C (60° F), they were also ideal for brewing beer, as happened on a large scale from the end of the 17th century until well into the 20th century. Several caves were dug especially for establishing breweries, and not just because of the ambient temperature: going underground allowed brewers to remain close to their customers without having to pay a premium for real estate up top.
Overview of the Paris Catacombs.Credit: Inspection Générale des Carrières, 1857 / Public domain.
At the end of the 19th century, the underground breweries of the 14th arrondissement alone produced more than a million hectoliters (22 million gallons) per year. One of the most famous of Paris' underground breweries, Dumesnil, stayed in operation until the late 1960s.
In that decade, the network of corridors and galleries south of the Seine, long since abandoned by miners, became the unofficial playground for the young people of Paris. They explored the fantastical world beneath their feet, in some cases via entry points located in their very schools. Fascinated, these cataphiles ("catacomb lovers") read up on old books, explored the subterranean labyrinth, and drew up schematics that were passed around among fellow initiates as reverently as treasure maps.
As Robert Macfarlane writes in Underland, Paris-beneath-their-feet became "a place where people might slip into different identities, assume new ways of being and relating, become fluid and wild in ways that are constrained on the surface."
Some larger caves turned into notorious party zones: a 7-meter-tall gallery below the Val-de-Grâce hospital is widely known as "Salle Z." Over the last few decades, various other locations in subterranean Paris have hosted jazz and rock concerts and rave parties — like no other city, Paris really has an "underground music scene."
Hokusai's Great Wave as the backdrop to the "beach" under Paris.Credit: Reddit
Cataphiles vs. cataphobes
With popularity came increased reports of nuisance and crime — the tunnels provided easy access to telephone cables, which were stolen for the resale value of their copper.
The general public's "discovery" of the underground network led the city of Paris to officially interdict all access by non-authorized persons. That decree dates back to 1955, but the "underground police" have an understanding with seasoned cataphiles. Their main targets are so-called tourists, who by their lack of knowledge expose themselves to risk of injuries or worse, and degrade their surroundings, often leaving loads of litter in their wake.
The understanding does not extend to the IGC. Unlike in the 19th century, when weak cavities were shored up by purpose-built pillars, the policy now is to inject concrete to fill up endangered spaces — thus progressively blocking off parts of the network. That procedure has also been used to separate the Catacombs to prevent "infiltration" of the site by cataphiles.
Many subterranean streets have their own names, signs and all. This is the Rue des Bourguignons (Street of the Burgundians) below the Champs des Capucins (Capuchin Field), neither of which exists on the surface.Credit: Jean-François Gornet via Wikimedia and licensed under
The cataphiles, however, are fighting back. In a game of cat and mouse with the authorities, they are reopening blocked passages and creating chatières ("cat flaps") through which they can squeeze into chambers no longer accessible via other underground corridors.
Catacomb climate control
Alone against the unstoppable tide of concrete, the amateurs of Underground Paris would be helpless. But the fight against climate change may turn the subterranean labyrinths from a liability into an asset — and the City of Paris into an ally.
The UN's 2015 Climate Plan — concluded in Paris, by the way — requires the world to reduce greenhouse gas emissions by 75 percent by 2050. And Paris itself wants to be Europe's greenest city by 2030. More sustainable climate control of our living spaces would be a great help toward both targets. A lot of energy is spent heating houses in winter and cooling them in summer.
This is where the constant temperature of the Parisian tunnels comes in. It's not just good for brewing beer; it's a source of geothermal energy, says Fieldwork, an architectural firm based in Paris. It can be used to temper temperatures, helping to cool houses in summer and warming them in winter.
One catch for the cataphiles: it also works when the underground cavities are filled up with concrete. So perhaps one day, Paris Underground, fully filled up with concrete, will completely fall off the map, reducing the city's formerly real doppelgänger into an air conditioning unit.
Cool in summer, warm in winter: Paris Underground could become Paris A/C.Credit: Fieldwork
Strange Maps #1083
Got a strange map? Let me know at email@example.com.
Meconium contains a wealth of information.
- A new study finds that the contents of an infants' first stool, known as meconium, can predict if they'll develop allergies with a high degree of accuracy.
- A metabolically diverse meconium, which indicates the initial food source for the gut microbiota, is associated with fewer allergies.
- The research hints at possible early interventions to prevent or treat allergies just after birth.
The prevalence of allergies arising in childhood has increased over the last 50 years, with 30 percent of the human population now having some kind of atopic disease such as eczema, food allergies, or asthma. The cause of this increase is still subject to debate, though it has been associated with a number of factors, including changes to the gut microbiomes of infants.
A new study by Canadian researchers published in Cell Reports Medicine may shed further light on how these allergies develop in children by examining the contents of their first diaper.
The things you do for science
The research team examined the first stool of 100 infants from the CHILD Cohort Study. The first stool of an infant is a thick, green, horrid-looking substance called meconium. It consists of various things that the infant ingests during the second half of gestation. Additionally, it provides not only a snapshot of what the infant was exposed to during that time, but it also reveals what the food sources will be for the initial gut bacteria that colonize the baby's digestive tract.
The content of the meconium was examined and found to contain such varied elements as amino acids, lipids, carbohydrates, and myriad other substances.
A graph of the comparative, summed abundance of different elements in a metabolic pathway after scaling to median abundance of each metabolite. The blue figures are those children without atopy, the yellow ones show the data for those with an atopic condition. Petersen et al.
The authors fed this information into an algorithm that used this data, along with the identities of the bacteria present as well as the baby's overall health, to predict which infants would go on to develop allergies within one year. The algorithm got it right 76 percent of the time.
A way to prevent childhood allergies?
Infants whose meconium had a less diverse metabolic niche the initial microbes to settle in the gut were at the highest risk of developing allergies a year later. Many of these elements were associated with the presence or absence of different bacterial groups in the digestive system of the child, which play an increasingly appreciated role in our overall health and development. The findings were summarized by senior co-author Dr. Brett Finlay:
"Our analysis revealed that newborns who developed allergic sensitization by one year of age had significantly less 'rich' meconium at birth, compared to those who didn't develop allergic sensitization."
The findings could be used to help understand how allergies form and even how to prevent them. Co-author Dr. Stuart Turvey commented on this possibility:
"We know that children with allergies are at the highest risk of also developing asthma. Now we have an opportunity to identify at-risk infants who could benefit from early interventions before they even begin to show signs and symptoms of allergies or asthma later in life."
A model for early childhood allergies
Petersen et al.
As shown above, the authors constructed a model of how they believe metabolites and bacterial diversity help prevent allergies. Increased diversity of metabolic products in the meconium encourage the development of "healthy" families of bacteria, like Peptostreptococcaceae, which in turn promote the development of a healthy and diverse gut microbiome. Ultimately, such diversity decreases the likelihood that a child will develop allergies.