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Inside the Netflix Recommendation Engine

Netflix makes a business out of getting subscribers to add tons of DVDs to a list of discs that will later be mailed out. Theoretically, the more discs in that list, the longer that subscriber will remain with the service, since new movies will just keep coming. So a big part of Netflix's business is recommending titles to subscribers based on what they've previously enjoyed. Netflix calls its recommendation system "Cinematch™."

In October 2006, Netflix announced The Netflix Prize, a $1 million cash award to anyone who could improve Cinematch™'s recommendation accuracy by 10%. What this "recommendation accuracy" bit means is: the system needs to get 10% better at predicting what a given user will think about a given movie, based on that user's prior movie preferences. Netflix asks users on its site to rank the movies it recommends (on a scale of 1 to 5 stars), and thus is able to mine this kind of data from daily usage.

Two weeks ago, The New York Times ran a fantastic article on Cinematch™ and The Netflix Prize. The Times profiled various programmers who are trying to improve the recommendation system's accuracy. Here's a snippet:

Each time he or his kids think of a new approach, [Len] Bertoni writes a computer program to test it. Each new algorithm takes on average three or four hours to churn through the data on the family's "quad core" Gateway computer. Bertoni's results have gradually improved. When I last spoke to him, he was at No. 8 on the leader board; his program was 8.8 percent better than Cinematch. The top team was at 9.44 percent. Bertoni said he thought he was within striking distance of victory.

But his progress had slowed to a crawl. The more Bertoni improved upon Netflix, the harder it became to move his number forward. This wasn't just his problem, though; the other competitors say that their progress is stalling, too, as they edge toward 10 percent. Why?

Bertoni says it's partly because of "Napoleon Dynamite," an indie comedy from 2004 that achieved cult status and went on to become extremely popular on Netflix. It is, Bertoni and others have discovered, maddeningly hard to determine how much people will like it. ...

Read the rest (and be sure to watch the accompanying video) for a surprisingly technical, but very readable, look into the technology behind recommendations.

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Today's Wine Glasses Are Almost Seven Times Larger Than They Were in 1700
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Holiday party season (a.k.a. hangover season) is in full swing. While you likely have no one to blame but yourself for drinking that second (or third) pour at the office soiree, your glassware isn't doing you any favors—especially if you live in the UK. Vino vessels in England are nearly seven times larger today than they were in 1700, according to a new study spotted by Live Science. These findings were recently published in the English medical journal The BMJ.

Researchers at the University of Cambridge measured more than 400 wineglasses from the past three centuries to gauge whether glass size affects how much we drink. They dug deep into the history of parties past, perusing both the collections of the Ashmolean Museum of Art and Archaeology at the University of Oxford and the Royal Household's assemblage of glassware (a new set is commissioned for each monarch). They also scoured a vintage catalog, a modern department store, and eBay for examples.

After measuring these cups, researchers concluded that the average wineglass in 1700 held just 2.2 fluid ounces. For comparison's sake, that's the size of a double shot at a bar. Glasses today hold an average of 15.2 fluid ounces, even though a standard single serving size of wine is just 5 ounces.

BMJ infographic detailing increases in wine glass size from 1700 to 2017
BMJ Publishing group Ltd.

Advances in technology and manufacturing are partly to blame for this increase, as is the wine industry. Marketing campaigns promoted the beverage as it increasingly became more affordable and available for purchase, which in turn prompted aficionados to opt for larger pours. Perhaps not surprisingly, this bigger-is-better mindset was also compounded by American drinking habits: Extra-large wineglasses became popular in the U.S. in the 1990s, prompting overseas manufacturers to follow suit.

Wine consumption in both England and America has risen dramatically since the 1960s [PDF]. Cambridge researchers noted that their study doesn't necessarily prove that the rise of super-sized glassware has led to this increase. But their findings do fit a larger trend: previous studies have found that larger plate size can increase food consumption. This might be because they skew our sense of perception, making us think we're consuming less than we actually are. And in the case of wine, in particular, oversized glasses could also heighten our sensory enjoyment, as they might release more of the drink's aroma.

“We cannot infer that the increase in glass size and the rise in wine consumption in England are causally linked,” the study's authors wrote. “Nor can we infer that reducing glass size would cut drinking. Our observation of increasing size does, however, draw attention to wine glass size as an area to investigate further in the context of population health.”

[h/t Live Science]

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Researchers Pore Over the Physics Behind the Layered Latte
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The layered latte isn't the most widely known espresso drink on coffee-shop menus, but it is a scientific curiosity. Instead of a traditional latte, where steamed milk is poured into a shot (or several) of espresso, the layered latte is made by pouring the espresso into a glass of hot milk. The result is an Instagram-friendly drink that features a gradient of milky coffee colors from pure white on the bottom to dark brown on the top. The effect is odd enough that Princeton University researchers decided to explore the fluid dynamics that make it happen, as The New York Times reports.

In a new study in Nature Communications, Princeton engineering professor Howard Stone and his team explore just what creates the distinct horizontal layers pattern of layered latte. To find out, they injected warm, dyed water into a tank filled with warm salt water, mimicking the process of pouring low-density espresso into higher-density steamed milk.

Four different images of a latte forming layers over time
Xue et al., Nature Communications (2017)

According to the study, the layered look of the latte forms over the course of minutes, and can last for "tens of minutes, or even several hours" if the drink isn't stirred. When the espresso-like dyed water was injected into the salt brine, the downward jet of the dyed water floated up to the top of the tank, because the buoyant force of the low-density liquid encountering the higher-density brine forced it upward. The layers become more visible when the hot drink cools down.

The New York Times explains it succinctly:

When the liquids try to mix, layered patterns form as gradients in temperature cause a portion of the liquid to heat up, become lighter and rise, while another, denser portion sinks. This gives rise to convection cells that trap mixtures of similar densities within layers.

This structure can withstand gentle movement, such as a light stirring or sipping, and can stay stable for as long as a day or more. The layers don't disappear until the liquids cool down to room temperature.

But before you go trying to experiment with layering your own lattes, know that it can be trickier than the study—which refers to the process as "haphazardly pouring espresso into a glass of warm milk"—makes it sound. You may need to experiment several times with the speed and height of your pour and the ratio of espresso to milk before you get the look just right.

[h/t The New York Times]

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