Thursday, March 7, 2013

Wright’s law (Economies Of Scale) Also Follow Moore's Law

Aeronautical engineer Theodore Wright, who pointed out that the cost of airplanes fell as the number of planes manufactured rose. Specifically, he said that the cost was proportional to the inverse of the number of planes manufactured raised to some power. This theory has since been put forward as a more general law that governs the costs of technological products, and is often explained on the basis that, the more we make, the better and more efficient we get at making.

Costs fall purely because of economies of scale. All these ‘laws’ predict that costs will fall over time, but each suggests a slightly different rate. “These hypotheses haven’t really been tested against data before,” says MIT's Jessika Trancik. She and her collaborators collected data for 62 technologies, ranging from chemicals production to energy devices (such as photovoltaic cells) and information technologies, spanning periods of between 10 and 39 years. “Assembling a large enough data set was a big challenge,” says Trancik.

The researchers evaluated the performance of each six such ‘laws’ using hindcasts — use of earlier data to predict later costs — and then looked at how these compared with the actual figures.

In fact, the laws didn't differ much at all. The most accurate was Wright’s law, but Moore’s law was close behind, at least for a relatively modest time horizon of a few decades. The predictions were so similar for these two laws, in fact, that the researchers suspected they might be related.

A link seems quite likely. In 1979, political scientist Devendra Sahal pointed out that if production of an item grows at an exponential rate, then Wright’s law and Moore’s law are equivalent. The data confirm that production does indeed grow exponentially for a wide range of products. “You wouldn’t necessarily expect that,” says Trancik.

That Moore’s law applies at all to so many different industries is a surprise, since computing has often been regarded as a special case. “It’s a much more general thing,” says author Doyne Farmer, currently at the University of Oxford, UK.


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