For a more extensive treatment, see Porter (1998a), which also contains an extensive bibliography on clusters and cluster initiatives.

For company and institutional implications, see Porter (1998a)

For a recent example, see Cairncross (1997)

Readers can find a full treatment of the intellectual roots of cluster thinking in Porter (1998a)

Enright (1993) illustrates the varying geographic scope of clusters.

Overly restrictive or overly extensive definitions of clusters can obscure the influence of clustering and lead to flawed statistical results. For example, SuarezVilla and Walrod (1997) state, "An establishment located in a cluster was, at most, within one quarter of a mile of the nearest one" (p. 1349). A more appropriate boundary in the field investigated probably is location within the same metropolitan area, so it is not surprising that the authors' statistical tests do not reveal the benefits of clustering

The same issues apply to cities, states, or regions within nations. This discussion will be primarily set at the level of the nation, although internal specialization and trade among states within larger nations prove to he an important determinant of prosperity