The share of U.S. patents that include at least one woman as an inventor has tripled over the last 30 years. But even with that increase, women inventors still made up only 12 percent of all inventors on U.S. patents granted in 2016.

Those were a couple of headline findings in a U.S. Patent and Trademark Office study released Tuesday. It found that women are making only the smallest of inroads in the patenting space.

“Even though more patent inventor teams include women, the gender composition among all inventors has not changed significantly” over the last 20 years, the authors of “Progress and Potential: A Profile of Women Inventors” conclude. The study was conducted by the USPTO's Office of the Chief Economist under the auspices of last fall's SUCCESS Act.

The report finds that women inventors have been growing their relative share of patents most quickly in the chemistry and design areas, while growth has been more sluggish in mechanical and electrical engineering.

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“Most of the growth is in the technologies and organizations where women have historically been more likely to innovate,” the study states. “Such trends suggest that women are specializing in technology fields and sectors where female predecessors have patented before rather than entering into male-dominated fields or firms.”

Women increased their share of patents at universities, hospitals and public research organizations. But they were represented on only about 10 percent of the inventions patented by businesses, which accounts for most patenting in the U.S.

Procter & Gamble Co., Bristol-Myers Squibb Co. and Abbott Laboratories had the highest rate of women on their patents over the last decade—ranging from 20 percent to 30 percent—while industrial companies such as Deere & Co. and Caterpillar Inc. scored the lowest, at about 5 percent. Large technology companies generally fell in the middle, ranging from 16 percent at IBM Corp., 11 percent at Google Inc., 10 percent at Amazon.com Inc and Cisco Systems Inc., and 8 percent at Apple Inc.

In terms of raw numbers, IBM employs the most women inventors at about 4,500, with Microsoft second at 2,300.

Julie Mar-Spinola, a former chairwoman of women's technology networking ChIPs and current member of the PTO's Patent Public Advisory Committee, said the statistics are “disappointing, not particularly surprising and still perplexing.”

Mar-Spinola, who is the chief IP officer at Finjan Holdings Inc., said a deeper dive into how companies run their patenting programs might provide more insight.

Terri Shieh-Newton, a Mintz, Levin, Cohn, Ferris, Glovsky and Popeo partner who helps companies build patent portfolios, said the big tech companies produce such a disproportionate share of the nation's patents that underrepresentation there would drag down the overall numbers.

Some companies employ a lot of women in research and development, Shieh-Newton said, but they're not always included in the brainstorming sessions that lead to the conception of new ideas. “If you're not in that room being part of that discussion, then you're not going to be an inventor” for purposes of a patent, she said.

The SUCCESS Act stands for Study of Underrepresented Classes Chasing Engineering and Science Success. It extended the PTO's fee-setting authority while requiring that the agency undertake studies on the numbers of patents applied for and obtained by women, minorities and veterans, and provide legislative recommendations to increase them.

The legislation came together quickly after a widely publicized Yale School of Management study last spring found that the PTO was more likely to reject women inventors' patents than those filed by teams of men. Sen. Mazie Hirono quizzed PTO director Andrei Iancu about the study at a Judiciary Committee hearing last year.

“The more innovators we can encourage, the more innovation this country will have and the entire economy will grow,” Iancu told Hirono at the time.

In a statement accompanying Monday's report, Iancu said that “it is important for the United States to broaden its innovation ecosphere demographically, geographically, and economically.”

“The USPTO will continue to push the national dialogue on this issue and do what we can to spur real change,” Iancu said.