Changes

**For each litigated patent, another was chosen at random from the set of all patents with the same application year and primary three-digit USPC assignment(thus controlling for technology and cohort effect).

* For each litigated and matched patent the following characteristics

# Technology field: the first assigned USPC class

# Citations

# Ownership: Individual, listed/unlisted company.

# Relative size of potential disputants: measure of the asymmetry in portfolio size between a patentee and a representative disputant he can expect to face on each patent.Let $Z_{cf}$ be the portfolio size for firm $f$ in technology class $c$, and let $Z_c = \sum_f Z_{cf}$ denote all patents in the class. $Z_f = \sum_c Z_{cf}$ is the portfolio size for firm $f$ $Z_c^* Z_c / n_c$ is the average portfolio size of the $n_c$ firms with patents in class $c$.The relative portfolio size of firm $f$ for patent $ i$ is given by:$R_{if} = Z_f /\sum_c w_{ci} Z_c^*$, where $w_ci = F_{ci}/F_i$ is the fraction of forward citations to patent $i$ that falls into technology class $c$.

# Technology concentration

==Model==