University Patenting: Estimating the Diminishing
Breadth of Knowledge Diffusion and Consumption
by Carlos Rosell and Ajay Agrawal
Comments by Mark Schankerman
(LSE and CEPR)
Does university patenting and technology management
restrict the dissemination of university-based knowledge?
Empirical formulation: Are university patented inventions
increasingly cited by a more concentrated set of
subsequent patentees, relative to corporate patents?
Why is this interesting?
1. Knowledge may be interesting/useful to a smaller or
more concentrated set of firms
2. Knowledge may be more restricted by university tech
management for income maximisation objectives
Paper is original, and the authors do a very nice, careful job
of demonstrating that the answer is yes to the empirical
Moreover, the narrowing (increase in assignee
concentration) of cites is mainly due to heavy patenting
(‘experienced) universities; thus probably not transitional.
Overall the finding is robust and I believe it.
But in my view the authors cannot tell distinguish between
hypotheses 1 and 2, so there is no basis to claim that
dissemination for downstream use is restricted (patent
thicket problem exacerbated) on this evidence.
Approach: Difference in differences regression framework,
comparing fragmentation of backward cites for universities
to corporate patents, and the same for forward cites.
For forward cites: patents issued in 1980-83 and 1986-89
For backward cites: patents applied for in 1980-83 and
Truncation issues probably second order (though citing
distributions do differ for university and non-university
Authors are careful to control for patent characteristics,
including tech field, originality, and generality. Thus their
finding of increased concentration of cites to university
patents is not due to reduced generality of patents.
Some Queries and Suggestions
• Why the specific periods chosen? Large samples, so
authors can include multiple time windows to identify
the fuller pattern of changes.
• If the concern is patent thickets and complementary
technologies (PTCT), then we should examine whether
the increased concentration is stronger in ‘complex’
tech areas (e.g. semiconductors, software) relative to
‘linear’ tech like pharmaceuticals.
Authors interact tech class dummies with the period
dummy, but do not ask if the coefficients link to the
complexity issue. Also could interact tech class with
• If the issue is PTCT, then the offending patents should
be the ones still in force. Lapsed patents create no
hold-up or licensing problem. Can authors distinguish
cites to patents still in force versus those to lapsed
patents? If their interpretation is right (it is about
strategic restriction), shouldn’t their finding be stronger
(only present?) for cites to in-force patents.
• I am unclear why backward and forward cites are
symmetrical for your argument. Why should backward
cite concentration reflect licensing behavior, even
under the null hypothesis that strategic restriction
through licensing occurs?
• Would be useful to have information on use of exclusive
v non-exclusive licensing by universities over time --
direct evidence linking to nature of licensing activity. If
the authors’ interpretation is right, use of exclusive
should be growing. AUTM data has such information for
1990’s and I don’t think it shows that.
My central concern about how to interpret the interesting
empirical finding in the paper is this:
Patent cites are references to prior art. They constrain
the property rights in the citing patent by circumscribing
the scope of allowable claims. We also think they tell us
something about patterns of sequential (cumulative)
But cites do NOT imply anything directly about
1. complementarity in production: Do I need to license
your patent to implement mine?
2. complementarity in research: Did I need to license
your patent to conduct the research that generated
Thus, observing fewer assignees citing university
patents does not by itself mean that the
dissemination of university patents for
downstream use is narrowing.
Original, well executed paper that delivers
new, interesting findings.
Interpretation: jury is still out, more needs to
In summary: we now know something new.
We are just not sure what it is.