Centers for Disease Control and Prevention data were used to describe 1980 -2007 trends among children 0 to 17 years of age and recent patterns according to gender, race, and age. Asthma period prevalence increased by 4.6% per year from 1980 to 1996. New measures introduced in 1997 show a plateau at historically high levels; 9.1% of US children (6.7 million) currently had asthma in 2007. Ambulatory care visit rates fluctuated during the 1990s, whereas emergency department visits and hospitalization rates decreased slightly. Asthma-related death rates increased through the middle 1990s but decreased after 1999. Recent data showed higher prevalence among older children (11-17 years), but the highest rates of asthmarelated health care use were among the youngest children (0 -4 years). After controlling for racial differences in prevalence, disparities in adverse outcomes remained; among children with asthma, non-Hispanic black children had greater risks for emergency department visits and death, compared with non-Hispanic white children. For hospitalizations, for which Hispanic ethnicity data were not available, black children had greater risk than white children. However, nonemergency ambulatory care use was lower for non-Hispanic black children. Although the large increases in childhood asthma prevalence have abated, the burden remains large. Potentially avoidable adverse outcomes and racial disparities continue to present challenges. These findings suggest the need for sustained asthma prevention and control efforts for children. Pediatrics 2009;123:S131-S145

This paper formulates the optimal control problem for a class of mathematical models in which the system to be controlled is characterized by a finite-state discrete-time Markov process. The states of this internal process are not directly observable by the controller; rather, he has available a set of observable outputs that are only probabilistically related to the internal state of the system. The formulation is illustrated by a simple machine-maintenance example, and other specific application areas are also discussed. The paper demonstrates that, if there are only a finite number of control intervals remaining, then the optimal payoff function is a piecewise-linear, convex function of the current state probabilities of the internal Markov process. In addition, an algorithm for utilizing this property to calculate the optimal control policy and payoff function for any finite horizon is outlined. These results are illustrated by a numerical example for the machine-maintenance problem.

This paper treats the discounted cost, optimal control problem for Markov processes with incomplete state information. The optimization approach for these partially observable Markov processes is a generalization of the well-known policy iteration technique for finding optimal stationary policies for completely observable Markov processes. The state space for the problem is the space of state occupancy probability distributions (the unit simplex). The development of the algorithm introduces several new ideas, including the class of finitely transient policies, which are shown to possess piecewise linear cost functions. The paper develops easily implemented approximations to stationary policies based on these finitely transient policies and shows that the concave hull of an approximation can be included in the well-known Howard policy improvement algorithm with subsequent convergence. The paper closes with a detailed example illustrating the application of the algorithm to the two-state partially observable Markov process.

The overall improvement in the health of Americans over the 20th century is best exemplified by dramatic changes in 2 trends: 1) the age-adjusted death rate declined by about 74%, while 2) life expectancy increased 56%. Leading causes of death shifted from infectious to chronic diseases. In 1900, infectious respiratory diseases accounted for nearly a quarter of all deaths. In 1998, the 10 leading causes of death in the United States were, respectively, heart disease and cancer followed by stroke, chronic obstructive pulmonary disease, accidents (unintentional injuries), pneumonia and influenza, diabetes, suicide, kidney diseases, and chronic liver disease and cirrhosis. Together these leading causes accounted for 84% of all deaths. The size and composition of the American population is fundamentally affected by the fertility rate and the number of births. From the beginning of the century there was a steady decline in the fertility rate to a low point in 1936. The postwar baby boom peaked in 1957, when 123 of every 1000 women aged 15 to 44 years gave birth. Thereafter, fertility rates began a steady decline. Trends in the number of births parallel the trends in the fertility rate. Beginning in 1936 and continuing to 1956, there was precipitous decline in maternal mortality from 582 deaths per 100 000 live births in 1935 to 40 in 1956. Since 1950 the maternal mortality ratio dropped by 90% to 7.1 in 1998. The infant mortality rate has shown an exponential decline during the 20th century. In 1915, approximately 100 white infants per 1000 live births died in the first year of life; the rate for black infants was almost twice as high. In 1998, the infant mortality rate was 7.2 overall, 6.0 for white infants, and 14.3 for black infants. For children older than 1 year of age, the overall decline in mortality during the 20th century has been spectacular. In 1900, >3 in 100 children died between their first and 20th birthday; today, <2 in 1000 die. At the beginning of the 20th century, the leading causes of child mortality were infectious diseases, including diarrheal diseases, diphtheria, measles, pneumonia and influenza, scarlet fever, tuberculosis, typhoid and paratyphoid fevers, and whooping cough. Between 1900 and 1998, the percentage of child deaths attributable to infectious diseases declined from 61.6% to 2%. Accidents accounted for 6.3% of child deaths in 1900, but 43.9% in 1998. Between 1900 and 1998, the death rate from accidents, now usually called unintentional injuries, declined two-thirds, from 47. 5 to 15.9 deaths per 100 000. The child dependency ratio far exceeded the elderly dependency ratio during most of the 20th century, particularly during the first 70 years. The elderly ratio has gained incrementally since then and the large increase expected beginning in 2010 indicates that the difference in the 2 ratios will become considerably less by 2030. The challenge for the 21st century is how to balance the needs of children with the growing demands for a large aging population of elderly persons.