The Believing Brain - Michael Shermer [137]
Nevertheless, the fact that our beliefs are so heavily laden with emotional baggage should give one pause to at least consider the position of others and to be skeptical of one’s own beliefs. The fact that we tend not to do so is a result of some very powerful cognitive biases that work to ensure that we are always right. I will examine them in the next chapter.
12
Confirmations of Belief
Have you ever gone to the phone to call a friend, only to have the phone ring first and find your friend on the other end of the line? What are the odds of that? Not high, and your patternicity intuition probably signaled to you that there was something special about this event. Was there? Probably not. Here’s why: the sum of all probabilities equals one. Given enough opportunities, outlier anomalies will inevitably happen. The question is not What is the probability that a friend would phone while being thought about?—which is very low—but In the total population of all people making phone calls and thinking about friends, what is the probability that at least one phone call will overlap with at least one simultaneous thought? which is very high. Analogously, the chance of any one person winning the lottery is extremely low, but in the lottery system as a whole, someone will win.
In his insightful book The Drunkard’s Walk, the mathematician and science writer Leonard Mlodinow computed the odds of a mutual fund manager named Bill Miller beating Standard & Poor’s 500 index fifteen years in a row.1 For this feat Miller was hailed as “the greatest money manager of the 1990s” and CNN computed the odds of him doing so at 372,529 to 1. Those are long odds indeed. And Mlodinow notes that if you had picked Bill Miller at the start of the streak in 1991 and computed the odds of him beating the S&P 500 every year for the next fifteen years, they would indeed be very slim. But this principle would apply to any mutual fund manager that you happened to pick. “You would have had the same odds against you if you had flipped a coin once a year for fifteen years with the goal of having it land heads up each time,” Mlodinow notes. But, in fact, there are more than six thousand mutual fund managers, “so the relevant question is, if thousands of people are tossing coins once a year and have been doing so for decades, what are the chances that one of them, for some period of fifteen years or longer, will toss all heads?” That probability is much higher. In fact, Mlodinow demonstrates that over the past forty years of active mutual fund trading, the odds that at least one mutual fund manager would beat the market every year for fifteen years in a row turn out to be about three out of four, or 75 percent!
I have applied this principle of probability thinking to miracles. Let us define a miracle as an event with million-to-one odds of occurring (intuitively that seems rare enough to earn the moniker). Let us also assign a number of one bit per second of data that flows into our senses as we go about our day, and assume that we are awake for twelve hours a day. That nets us 43,200 bits of data per day, or 1,296,000 per month. Even assuming that 99.999 percent of these bits are totally meaningless (and so we filter them out or forget them entirely), that still leaves 1.3 “miracles” per month, or 15.5 miracles per year. Thanks to selective memory and the confirmation bias, we will remember only those few astonishing coincidences and forget the vast sea of meaningless data.
We can employ a similar back-of-the-envelope calculation to explain death premonition dreams. The average person has about five dreams per night, or 1,825 dreams per year. If we remember only a tenth of our dreams, then we recall 182.5 dreams per year. There are about 300 million Americans, who thus produce 54.7 billion remembered dreams per year. Sociologists tell us that each of us knows about 150 people fairly well, thus producing a network social grid of 45 billion personal relationship connections. With an annual death rate of 2.4 million Americans per year (all ages,