Change in the population of health systems: From 1985 to 1998

This article compares the predictions in Stephen Shortell's 1988 seminal ar ticle, The Evolution of Hospital Systems: Unfulfilled Promises and Self-Ful filling Prophesies, with current data on health systems over a 14-year peri od from 1985 to 1998. Specifically, we review five of Shortell's prediction s related to the horizontal growth of health systems and compare these pred ictions with empirical data on structural changes in the population of heal th systems. Our analyses suggest that Shortell's predictions corresponded t o much of the actual behavior demonstrated in the population over the past one-and-a-half decades. Support was found for the following: (1) health sys tems form in two recurring stages; (2) previously unaffiliated hospitals ar e affiliating with existing systems rather than participating in the creati on of new systems; and (3) health systems have evolved into five different strata, each of which represents different shares of the population; such p opulation patterns have important implications for individual hospitals and health systems. By attending to patterns of change in the industry's socia l structure, hospitals and health systems can determine whether it is likel y to continue along past trajectories or whether it shows signs of change t hat may pave way for the breakdown of existing organizational forms, entry of new organizational players, and the emergence of new governance structur es.