Call it the paradox of stock options.

Companies that succeed in going public tend to “find that the quality of internal innovation declines” post-IPO, according to a meticulous new study (PDF) by Shai Bernstein, assistant finance professor at the Stanford Graduate School of Business. Not only does the level of innovation fall at newly public companies, but top inventors there tend to bail, the study found. Those who remain to watch their options vest, meanwhile, suffer “a decline in productivity.”

In reaching his conclusion, Bernstein analyzed the patent data of over 1,500 public and private U.S. technology firms between 1983 and 2006, a data set that includes Microsoft and Google, among others. This isn’t to say the publicly traded company hits an innovation wall post-IPO. But instead of fostering invention in-house, they tend to acquire expertise and innovation by buying up other companies. Hewlett-Packard investors can tell you how that works out.