Diversication: Similar to Mayers and Smith (1990), Choi and Weiss (2005), Cole and
McCullough (2006) and Leverty and Grace (2010), I have measured the concentration of the lines
of business and the states they operate in, using the Herndahl index to express both states and
lines of business. The Herndahl index has been used to characterize the market of each insurance
company in terms of geography and business type. The state Herndahl index for each company
can be written as,
where n is the total number of states. Under this denition, it represents several characteristics.
First, if the HerfindahlState is high, it means the company is focusing on particular states. On
the other hand, if the HerfindahlState is low, the company has diversied itself to many states,
but might face more competition in many states compared to businesses with a higher value of the
index. The insurer that has more concentration can enjoy the benet of reinsurance as a means
to diversify itself. However, the insurer that has less concentration does not need to buy more
reinsurance.