Many HIV prevalence surveys are plagued by the problem that a sizeable number of surveyed individuals do not consent to contribute blood samples for testing. One can ignore this problem, as is often done, but the resultant bias can be of sufficient magnitude to invalidate the results of the survey, especially if the number of non-responders is high and the reason for refusing to participate is ...

Surprisingly little is known regarding the human mixing patterns relevant to the spread of closecontact infections, such as measles, influenza and meningococcal disease. This study aims to estimate the number of partnerships that individuals make, their stability and the degree to which mixing is assortative with respect to age. We defined four levels of putative at-risk events from casual (phy...

In many areas of clinical investigation there is great interest in identifying and validating surrogate endpoints, biomarkers that can be measured a relatively short time after a treatment has been administered and that can reliably predict the effect of treatment on the clinical outcome of interest. However, despite dramatic advances in the ability to measure biomarkers, the recent history of ...

Background: Maternal morbidity is more common than maternal death, and population-based estimates of the burden of maternal morbidity could provide important indicators for monitoring trends, priority setting and evaluating the health impact of interventions. Methods based on lay reporting of obstetric events have been shown to lack specificity and there is a need for new approaches to measure ...

An ordinary differential equation x = f (t, x(t)) (ODE) uniquely assigns the time derivative x (t) = d dt x(t) as a function of t and x. A differential inclusion x ∈ F (t, x(t)), (DI) on the other hand, only requires that the derivative x be inside a given set F (t, x) ⊂ R n. Therefore, given an initial condition x(0) = ¯ x, one can usually find several solutions of (DI). f(x) x _ x _ x x F(x) ...

Background: Various methods have been proposed for sampling when data on the population are limited. However, these methods are often biased. We propose a new method to draw a population sample using Global Positioning Systems and aerial or satellite photographs. Results: We randomly sampled Global Positioning System locations in designated areas. A circle was drawn around each location with ra...