A study of Patent Thickets (1.31Mb) - UK Intellectual Property Office
A study of Patent Thickets (1.31Mb) - UK Intellectual Property Office
A study of Patent Thickets (1.31Mb) - UK Intellectual Property Office
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
A Study <strong>of</strong> <strong>Patent</strong> <strong>Thickets</strong> 75<br />
élog( t l ) ù<br />
i i<br />
log-normal: St ( ) = 1 -F s<br />
êë<br />
úû<br />
log-logistic: St ( ) = (1 + ( tl<br />
) )<br />
i<br />
1/ g -1<br />
i<br />
where S(t) is the survival function and λ i<br />
= exp(x i<br />
β). We allow the parameters σ (log-normal) or<br />
γ(log-logistic) to vary freely across industries. That is, for these models, both the mean and the<br />
variance <strong>of</strong> the survival distribution are specific to the 2-digit industry. In the case <strong>of</strong> these two<br />
models, the elasticity <strong>of</strong> the hazard with respect to a characteristic x depends on time and on<br />
the industry-specific parameter (σ or γ), yielding a more flexible model. Note also that the hazard<br />
rate is given by –dlogS(t)/dt in general (Lancaster 1990).
Change language