How fast is online learning evolving? Are wind turbines a promising investment? And how long before a cheap hoverboard makes it to market? Attempting to answer such questions requires knowing something about the rate at which a technology is improving. Now engineers at MIT have devised a formula for estimating how fast a technology is advancing, based on information gleaned from relevant patents.

The researchers determined the improvement rates of 28 different technologies, including solar photovoltaics, 3-D printing, fuel-cell technology, and genome sequencing. They searched through the U.S. Patent Office database for patents associated with each domain -- more than 500,000 total -- by developing a novel method to quickly and accurately select the patents that best represent each technology.

Once these were identified, the researchers analyzed certain metrics across patents in each domain, and found that some were more likely to predict a technology's improvement rate than others. In particular, forward citations -- the number of times a patent is cited by subsequent patents -- is a good predictor, as is the date of a patent's publication: Technologies with more recent patents are likely innovating at a faster rate than those with older patents.

The team devised an equation incorporating a patent set's average forward citation and average publication date, and calculated the rate of improvement for each technology domain. Their results matched closely with the rates determined through the more labor-intensive approach of finding numerous historical performance data points for each technology.

Among the 28 domains analyzed, the researchers found the fastest-developing technologies include optical and wireless communications, 3-D printing, and MRI technology, while domains such as batteries, wind turbines, and combustion engines appear to be improving at slower rates.

Chris Benson, a former graduate student in MIT's Department of Mechanical Engineering, says the new prediction tool may be of interest to venture capitalists, startups, and government and industry labs looking to explore new technology.

"There's a lot of nuance to our method, and I don't see it as something to hand out to the masses to play with," says Benson, who helped developed the prediction tool. "I see it more as something where we work with somebody to help them understand what the future technological capabilities that they're interested in are. We're probably more like a real estate agent, and less like Zillow."

Benson and Chris Magee, a professor of the practice of engineering systems at MIT, have published their results this week in the journal PLoS ONE. The paper contains the fundamental findings and equations relating technological improvement to a variety of patent characteristics.