DO PATENT POOLS ENCOURAGE INNOVATION? EVIDENCE ...

TABLE 4: OLS – DEPENDENT VARIABLE IS PATENTS PER SUBCLASS AND YEAR, 1921-1948
(1) (2) (3) (4) (5)
Pool*pool patents -0.338** -0.451** -0.412**
(0.098) (0.120) (0.118)
Pool*pool patents*years 1-5 -0.328**
(0.099)
Pool*pool patents*years 6-10 -0.491**
(0.148)
Pool*pool patents*years 11-18 -0.549**
(0.151)
Pool*pool cross-reference patents -0.102 -0.101
(0.086) (0.087)
Pool*pool subclass -0.555**
(0.156)
Pool*cross-reference subclass 0.101
(0.109)
Constant 0.947** 0.947** 0.947** 0.947** 0.947**
(0.008) (0.008) (0.008) (0.008) (0.008)
Subclass fixed effects Yes Yes Yes Yes Yes
Year fixed effects Yes Yes Yes Yes Yes
Linear and quadratic trends - Yes Yes Yes Yes
Standard errors clustered at the subclass level; ** significant at 1 percent, * significant at 5 percent.
N (# of subclasses * 28 years) 1,285,676 1,285,676 1,285,676 1,285,676 1,285,676
R-squared 0.526 0.526 0.526 0.526 0.526
Notes: Data include 45,917 subclasses in 103 main classes that include at least one pool patent. The timing of
invention is measured by the year of the patent application. The variable pool equals 1 for years after the pool
forms. Pool patents counts patents that were included in the initial pooling agreement and list subclass c as
primary (original) subclass. Cross-reference patents counts patents that list subclass c as a secondary (crossreference)
subclass. Pool subclass equals 1 for 371 subclasses that include at least one pool patent; cross-reference
subclass equals 1 for 534 subclasses that include at least one cross-reference patent but did not include any original
patents.
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