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The Pepsi Challenge has been an ongoing marketing promotion run by PepsiCo since 1975. It is also the name of a cross country ski race at Giant's Ridge Ski Area in Biwabik, Minnesota, an event sponsored by Pepsi.
The challenge originally took the form of a single blind taste test. At malls, shopping centers, and other public locations, a Pepsi representative sets up a table with two white cups: one containing Pepsi and one with Coca-Cola. Shoppers are encouraged to taste both colas, and then select which drink they prefer. Then the representative reveals the two bottles so the taster can see whether they preferred Coke or Pepsi. The results of the test leaned toward a consensus that Pepsi was preferred by more Americans.
In his book Blink: The Power of Thinking Without Thinking (2005), author Malcolm Gladwell presents evidence that suggests Pepsi's success over Coca-Cola in the "Pepsi Challenge" is a result of the flawed nature of the "sip test" method. His research shows that tasters will generally prefer the sweeter of two beverages based on a single sip, even if they prefer a less sweet beverage over the course of an entire can.
When the preference in blind tests is compared to tests wherein cups are labeled with arbitrary labels (e.g., S or L) or brand names, the ratings of preference change. Scientific findings do support a perceptible difference between Coca-Cola and Pepsi, but not between Pepsi and RC Cola.
In his book, Bad Habits, humorist Dave Barry describes the Pepsi challenge as, "Pepsi’s ongoing misguided attempt to convince the general public that Coke and Pepsi are not the same thing, which of course they are." 
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