Robust population management under uncertainty for structured population models.

Structured population models are increasingly used in decision making, but typically have many entries that are unknown or highly uncertain. We present an approach for the systematic analysis of the effect of uncertainties on long-term population growth or decay. Many decisions for threatened and endangered species are made with poor or no information. We can still make decisions under these circumstances in a manner that is highly defensible, even without making assumptions about the distribution of uncertainty, or limiting ourselves to discussions of single, infinitesimally small changes in the parameters. Suppose that the model (determined by the data) for the population in question predicts long-term growth. Our goal is to determine how uncertain the data can be before the model loses this property. Some uncertainties will maintain long-term growth, and some will lead to long-term decay. The uncertainties are typically structured, and can be described by several parameters. We show how to determine which parameters maintain long-term growth. We illustrate the advantages of the method by applying it to a Peregrine Falcon population. The U.S. Fish and Wildlife Service recently decided to allow minimal harvesting of Peregrine Falcons after their recent removal from the Endangered Species List. Based on published demographic rates, we find that an asymptotic growth rate lambda > 1 is guaranteed with 5% harvest rate up to 3% error in adult survival if no two-year-olds breed, and up to 11% error if all two-year-olds breed. If a population growth rate of 3% or greater is desired, the acceptable error in adult survival decreases to between 1% and 6% depending of the proportion of two-year-olds that breed. These results clearly show the interactions between uncertainties in different parameters, and suggest that a harvest decision at this stage may be premature without solid data on adult survival and the frequency of breeding by young adults.

Applications to undergraduate nursing courses.

Education of nurses has in recent years developed in centres of higher education, but with a rapid rise in courses offered concern has been expressed that too few suitable applicants may be available. This study has attempted to ascertain actual demand for the courses available by cross-referencing applications to a sample of courses, and has demonstrated a downward trend of suitable applications over the two years 1975 and 1976. A cautionary approach to establishing new courses or increasing numbers on existing courses may be advisable and further comparable work will be carried out to assess the validity of the trends already found.

Case-control method for seeking evidence of contagion in Crohn's disease.

All cases of Crohn's disease in the Nottingham area were ascertained and dates and places of domicile and work before and after onset of symptoms were noted. Similar information was taken from matched control subjects and the Pike and Smith (Biometrics 30:263-279, 1974) case control technique for evaluating clustering of patients in time and space was applied. These results do not support the infectious hypothesis.

The demographic and social characteristics of patients with Crohn's disease in the Nottingham area.

All 260 patients diagnosed as having Crohn's disease between 1958 and 1973, in the Nottingham area, were sought and demographic and social characteristics obtained by personal interview. These were compared with the general population, using the 1971 census data. We found significantly high proportions of patients who were female; married; in the age groups 20-39 and 60-54; and in managerial or skilled manual occupations.

Crohn's disease in Nottingham: a search for time-space clustering.

All cases of Crohn's disease in the Nottingham area were ascertained and the date and place of domicile and work at the time of onset of symptoms noted. Applying the Knox and Pike and Smith tests for clustering of patients in time and space, no significant results were observed. Further analysis of differences in time-space clustering between a group of patients and matched controls is in hand.