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Many compartment based epidemiological models are written as differential equation systems for various status subpopulation sizes with per person-time transfer rates between compartments. However, field data obtained by sampling at chosen times is usually provided in terms of status proportions from the total observable population (e.g., relative prevalence). Relationships between per person-time transfer rates (incidence, mortality, intervention rates) and proportions are not obvious when heterogeneity is at work because the various subpopulation sizes undergo different attrition rates and are not evolving in synchrony with the corresponding proportions. Rules are proposed to write sets of differential equations for compartment models, directly in terms of the proportions of the total observable at any time. To facilitate the writing of relationships between per person-time transfer rates and proportions, the systems are cast in network equivalent forms satisfying rules analogous to those of electrical networks (Kirchhoff's law for currents). The method is also extended to variability in the rates within a status subpopulation, considering either a fixed set of compartmental subdivisions or an inner continuum of differences in rates.

Although scaphoid fractures are relatively common encounters in orthopaedic and trauma surgery, the demographics of these injuries are not well studied. The classical teaching in the subject limits scaphoid fractures in the age between ten and 60 years (or 70 years in other sources). The incidence or the prevalence of scaphoid fractures in the elderly population is not focused on and not studied or explored.

We reviewed the literature for any available epidemiological studies of scaphoid fractures. We also sought the available data of scaphoid fractures in the elderly population in case series and case reports which have relevant data on the subject. Four epidemiological studies, two case series, and one case report are included. We discuss the available data in these articles and conclude that scaphoid fractures in the elderly, although rare, have been reported. However, there are not enough epidemiological studies to draw figures. Ignorance of this proportion of population could result in missed fractures in the elderly. Therefore, we encourage researchers to carry out epidemiological studies of scaphoid fractures with more focus on this population group.

Objective: To evaluate the association between vitamin supplements and the incidence and progression of radiographic knee osteoarthritis (OA). Study Design: Prospective cohort. Methods: Men and women aged 40 years and older (N = 2239) participating in the community-based Clearwater Osteoarthritis Study (1988–current) with biennial, sequential radiographs. The Lawrence & Kellgren ordinal scale was used to determine evidence of the study outcome, radiographic knee OA, and progression of radiographic knee OA. The study exposure was baseline history of self-reported vitamin supplement usage. Results: Individuals without baseline knee OA who self-reported vitamin supplement usage were 12% less likely to develop knee OA than were those individuals who self-reported no vitamin supplement usage (RR = 0.88; 95% C.I. 0.86–0.89). Those with baseline knee OA who self-reported vitamin supplement usage were 7% less likely to experience knee OA progression than were those individuals who self-reported no vitamin supplement usage (RR = 0.93; 95% C.I. 0.87–0.99). Conclusion: After consideration of BMI, gender, age, history of knee trauma, exercise and vitamin supplement usage prior to study baseline, these findings suggest that vitamin supplement usage may play a protective role in knee OA. Vitamin supplements may be a cost-effective strategy to reduce the incidence and/or slow the progression of knee OA. As many approved OA drugs are accompanied by adverse side effects, the role of vitamin supplements in the development and progression of knee OA warrants further investigation.

The class of fully semimonotone matrices is well known in the study of the linear complementarity problem. Stone [(1981) Ph.D. thesis, Dept. of Operations Research, Stanford University, Stanford, CA] introduced this class and conjectured that the principal minors of any fully semimonotone Q₀-matrix are non-negative. While the problem is still open, Murthy and Parthasarathy [(1998) Math. Program.82, 401–411] introduced the concept of incidence using which they proved that the principal minors of any matrix in the class of fully copositive Q₀-matrices, a subclass of fully semimonotone Q₀-matrices, are non-negative. In this paper, we study some properties of fully semimonotone matrices in connection with incidence. The main result of the paper shows that Stone's conjecture is true in the special case where the complementary cones have no partial incidence. We also present an interesting characterization of Q₀ for matrices with a special structure. This result is very useful in checking whether a given matrix belongs to Q₀ provided it has the special structure. Several examples are discussed in connection with incidence and Q₀ property.

Gastric cancer is the second most common cancer in the world. It is also the second most common cause of death from cancer. It has an uneven geographical distribution with incidence and mortality rates that vary greatly from high risk to low risk areas. Even within the same country, there may be variations associated with regional differences or ethnic composition. Time trends over the last few decades reveal a decreasing incidence and mortality. All these, together with incidence and mortality patterns in migrant populations, point to a predominantly environmental etiology in gastric cancer. Gastric cancer carries a poor prognosis with global 5-year survival of less than 20%. Gastric cancer will remain a sizeable healthcare problem for many more years.

The accumulation of genetic alterations causes cancers. Since this accumulation takes time, the incidence of most cancers is thought to increase exponentially with age. However, careful measurements of the age-specific incidence show that the specific incidence for many forms of cancer rises with age to a maximum, and then decreases. This decrease in the age-specific incidence with age is an anomaly. Understanding this anomaly should lead to a better understanding of how tumors develop and grow. Here we derive the shape of the age-specific incidence, showing that it should follow the shape of a Weibull distribution. Measurements indicate that the age-specific incidence for colon cancer does indeed follow a Weibull distribution. This analysis leads to the interpretation that for colon cancer two subpopulations exist in the general population: a susceptible population and an immune population. Colon tumors will only occur in the susceptible population. This analysis is consistent with the developmental origins of disease hypothesis and generalizable to many other common forms of cancer.

The use of a less sensitive or detuned test for recent human immunodeficiency virus (HIV) infection requires some modification to the standard incidence estimator. We use a stochastic simulation to demonstrate the details of using a detuned test to estimate incidence. We calculate the probabilities of the outcomes and give the result of the simulation as an example. Two estimators are compared and recommendations are made for calculating confidence intervals. We also show that the window period should be chosen to be half the collection period in order to minimize bias in the incidence estimator.

No abstract received.

This note is concerned with estimating the number of SARS cases in the 2002–3 epidemic in mainland China. Some recorded data from Hong Kong, and partial data from the mainland are used, while SARS incidence is modelled by a Beta function in order to derive likely outcomes. The conclusion is that there were many more cases of SARS in mainland China than were officially recorded.