Bad Data

Abstract

When I first started teaching economics in 1971, my wife’s grandfather (“Popsie”) knew that my Ph.D. thesis used Yale’s big computer to estimate an extremely complicated economic model. Popsie had bought and sold stocks successfully for decades. He even had his own desk at his broker’s office where he could trade gossip and stocks. Nonetheless, he wanted advice from a 21-year-old kid who had no money and had never bought a single share of stock in his life—me—because I worked with computers. “Ask the computer what it thinks of Schlumberger.” “Ask the computer what it thinks of GE.” This naive belief that computers are infallible has been around ever since the first computer was invented more than 100 years ago by Charles Babbage. While a teenager, the great French mathematician Blaise Pascal built a mechanical calculator called the Arithmetique to help his father, a French tax collector. The Arithmetique was a box with visible dials connected to gears hidden inside the box. Each dial had ten digits labeled 0 through 9.When the dial for the 1s column moved from 9 to 0, the dial for the 10s column moved up 1 notch; when the dial for the 10s column moved from9 to 0, the dial for the 100s column moved up 1 notch; and so on. The Aritmatique could do addition and subtraction, but the dials had to be turned by hand. Babbage realized that he could convert complex formulas into simple addition-and-subtraction calculations and automate the calculations, so that a mechanical computer would do the calculations perfectly every time, thereby eliminating human error. Babbage’s first design was called the Difference Engine, a steam powered behemoth made of brass and iron that was 8 feet tall, weighed 15 tons, had 25,000 parts. The Difference Engine could make calculations up to 20 decimals long and it could print formatted tables of results. After a decade tinkering with the design, Babbage began working on plans for a more powerful calculator he called the Analytical Engine. This design had more than 50,000 components, used perforated cards to input instructions and data, and could store up to one thousand 50-digit numbers.