822 International Organization lasts at least twenty years;most of these countries,in fact,sign BITs throughout the forty-year period.Spain is an exception,with a short spate of BITs in the 1990s only.Potential hosts,however,demonstrate a different pattern:their BIT signings spike up in a more clustered pattern,one indicative of programmatic activ- ity (see Figure 5).27 Evidence of programmatic activity can be established statistically as well.Com- paring the average kurtosis28 for the historical distribution of BITs among both home and host countries,it is clear that the distribution of BITs over the past forty years is significantly more peaked(less uniform)for the host than it is for home countries (9.11 and 4.48,respectively).The standard deviation of their distribu- tions over time is also lower for host countries than it is for home (7.08 versus 9.39,respectively),suggesting a more clustered pattern of activity for the host.If BITs are driven by home country programs,it is not especially apparent in the data.Rather,it appears that potential hosts are more likely to sign in clusters- suggesting that while the major capital exporters stand ready with model treaties in hand,the decision whether and when to sign is left to a large extent to the host. The notion that home countries make take-it-or-leave-it offers to potential hosts and that hosts eventually decide to sign BITs is also consistent with the observed content of BITs.These treaties tend to provide consistent terms,even across dif- ferent home countries.In particular,the core terms of the treaties are almost always present:mandatory dispute resolution before an international arbitration body,a private right of action for investors,monetary compensation in the event of a vio- lation,national treatment,and most-favored-nation treatment.This uniformity sug- gests that host countries are"price-takers"with respect to the terms of these treaties, consistent with our assumptions.In essence,each home country has market power over the terms that will govern investment by its locals.Host countries,on the other hand,realize that they must compete with other potential hosts and,there- fore,cannot demand changes to the core provisions of the treaties. A Competitive Theory of BIT Diffusion Our theory of BIT diffusion29 has a simple structure.BITs are viewed by host governments and by investors as devices that raise the expected return on invest- ments.The treaties do this by assisting governments in making credible commit- ments to treat foreign investors"fairly"-as described in the previous section.BITs 27.Appendixes I and 2,available online at(https://netfiles.uiuc.edu/zelkins/www),also orga- nized by capital-exporting and -importing countries,summarize the BIT history for all 178 countries that have ever signed a BIT. 28.Kurtosis is the degree to which a distribution is peaked,or clustered,with high kurtosis indi- cating clustered data,and low kurtosis indicating a more uniform distribution. 29.See Elkins and Simmons 2005,for a further elaboration of the concept of "diffusion."lasts at least twenty years; most of these countries, in fact, sign BITs throughout the forty-year period+ Spain is an exception, with a short spate of BITs in the 1990s only+ Potential hosts, however, demonstrate a different pattern: their BIT signings spike up in a more clustered pattern, one indicative of programmatic activ￾ity ~see Figure 5!+ 27 Evidence of programmatic activity can be established statistically as well+ Com￾paring the average kurtosis28 for the historical distribution of BITs among both home and host countries, it is clear that the distribution of BITs over the past forty years is significantly more peaked ~less uniform! for the host than it is for home countries ~9+11 and 4+48, respectively!+ The standard deviation of their distribu￾tions over time is also lower for host countries than it is for home ~7+08 versus 9+39, respectively!, suggesting a more clustered pattern of activity for the host+ If BITs are driven by home country programs, it is not especially apparent in the data+ Rather, it appears that potential hosts are more likely to sign in clusters— suggesting that while the major capital exporters stand ready with model treaties in hand, the decision whether and when to sign is left to a large extent to the host+ The notion that home countries make take-it-or-leave-it offers to potential hosts and that hosts eventually decide to sign BITs is also consistent with the observed content of BITs+ These treaties tend to provide consistent terms, even across dif￾ferent home countries+ In particular, the core terms of the treaties are almost always present: mandatory dispute resolution before an international arbitration body, a private right of action for investors, monetary compensation in the event of a vio￾lation, national treatment, and most-favored-nation treatment+ This uniformity sug￾gests that host countries are “price-takers” with respect to the terms of these treaties, consistent with our assumptions+ In essence, each home country has market power over the terms that will govern investment by its locals+ Host countries, on the other hand, realize that they must compete with other potential hosts and, there￾fore, cannot demand changes to the core provisions of the treaties+ A Competitive Theory of BIT Diffusion Our theory of BIT diffusion29 has a simple structure+ BITs are viewed by host governments and by investors as devices that raise the expected return on invest￾ments+ The treaties do this by assisting governments in making credible commit￾ments to treat foreign investors “fairly”—as described in the previous section+ BITs 27+ Appendixes 1 and 2, available online at ^https:00netfiles+uiuc+edu0zelkins0www&, also orga￾nized by capital-exporting and -importing countries, summarize the BIT history for all 178 countries that have ever signed a BIT+ 28+ Kurtosis is the degree to which a distribution is peaked, or clustered, with high kurtosis indi￾cating clustered data, and low kurtosis indicating a more uniform distribution+ 29+ See Elkins and Simmons 2005, for a further elaboration of the concept of “diffusion+” 822 International Organization