Have you noticed the word “Classic” beside the Coca Cola logo in some of its products? What is so classical about a can of coke?
In 1980s, Pepsi launched an aggressive advertising campaign to boost sales. People at my age would probably remember television advertisements featuring a boy or girl trying two cups of unlabelled coke and being asked to choose the better one. After he/she had made the decision, the better coke always turned out to be Pepsi. You may think this is rubbish. We can always hire an actor to do this, right?
The Coca Cola Company certainly did not trust it either. However, being a big company, it decided to be cautious and secretly performed similar tests on volunteers. Much to their distress, Pepsi really seemed to be winning. Over 60% of testers thought Pepsi tasted better. The company saw this as a potential disaster, and quickly changed the formula of the drink with “New Coke” on 23 April 1985.
The result? The company converted a potential disaster to a real one. Customers just hated the new products and protested. Sales dropped. The company quickly returned back to the original formula in less than 3 months. To be absolutely sure that the customers were pleased, it added the word “Classic” next to the logo.
What went wrong? In a sip test, a tester only takes a mouthful of soft drink. The sweeter product is more likely to win. In real life, people drink the whole can of coke, not a sip. In such settings, it may taste too sweet.
Therefore, you must understand what an investigation is measuring before you can use it. Misusing an investigation is not useless. It is worse than useless. It is misleading.
Some weeks ago, I noticed a young doctor checking blood for carcinoembryonic antigen in a patient with anemia. “This is not supposed to be a screening or diagnostic test,” I said.
“A positive test increases our suspicion of colorectal cancer,” the doctor protested. “Taking some blood causes no harm anyway.”
“No,” I disagreed, “you can still harm the patient. Imagine what would happen if you decide not to perform endoscopy to rule out cancer if the blood test is negative.”