DO PATENT POOLS ENCOURAGE INNOVATION? EVIDENCE ...

egressions that control for the count data properties of patent data, and alternative
OLS and Poisson estimates that control for the quality of patents.
Regressions that drop individual pools from the sample indicate that the
observed effects are not driven by a single pool. Dropping aircraft instruments
and variable condensers yields to the largest decline in estimated effects, but
estimates remain large and statistically significant. Without aircraft instruments
the estimated decline is -0.38 (instead of -0.45) patents per subclass and year;
without variable condensers it is -0.42 patents per subclass and year.
An additional test explores variation in the estimated decline across
subclasses with a single pool patent and subclasses with two or more pool patents.
In subclasses with one pool patent, the technology was already owned by a single
firm so that the creation of a pool may not have had any direct effect (even though
the technology may be affected by complementarities and spillovers from other
subclasses). In subclasses with two or more pool patents, however, the creation of
a pool may have affected the ownership structure, and eliminated competition.
Consistent with this idea, patent data confirm that the decline in patenting after
the creation of the pool was significantly stronger for subclasses that included two
or more pool patents.
Finally, a descriptive analysis examines correlations between the rate of
decline in patenting and specific pool characteristics, such as their openness to
licensing, grant-back rules that require members to offer all new patents to the
pool (Lerner and Tirole, 2004), and the inclusion of members from other
countries. Openness to licensing is correlated with a stronger negative effect,
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