There are a bunch of cool new articles in PLoS Medicine, PLoS Biology and PLoS Neglected Tropical Diseases today. Take a look:
The Dirty War Index: Statistical Issues, Feasibility, and Interpretation:
In this issue of PLoS Medicine, Madelyn Hsiao-Rei Hicks and Michael Spagat propose a new quantitative tool [1] in the emerging field of human security sciences [2]. Quantitative data about people's insecurity can lead to objective knowledge about many of the contexts of violence in the world today. Thus developing quantitative tools for use in this domain is important.
Hicks and Spagat's tool is called the Dirty War Index (DWI), which "systematically identifies rates of particularly undesirable or prohibited, i.e., "dirty," war outcomes inflicted on populations during armed conflict" [1]. After choosing a relevant public health outcome, a DWI is calculated as the ratio of "the number of dirty cases" of an outcome to the "total number of cases." There are many moral and legal questions regarding the division of acts of violence in armed conflict into those that are "dirty" and those--presumably--that are not "dirty." I am not addressing these questions here. Instead, I will discuss some statistical issues that may arise in calculating a DWI, and the feasibility and interpretation of DWIs.
Documentation, analysis, and prevention of the harmful effects of armed conflict on populations are established public health priorities [1-5]. Although public health research on war is increasingly framed in human rights terms [6-13], general public health methods are typically applied without direct links to laws of war. Laws of war are international humanitarian laws and customary standards regarding the treatment of civilians and combatants, mainly described in the four Geneva Conventions of 1949 and their Additional Protocols I and II regarding international and civil conflicts [14]. With notable exceptions [11,15-17], absolute numbers are usually reported (e.g., number of persons killed), without systematic description of the proportional effects of armed conflict, thereby limiting the utility of findings and scope of interpretation.
A New Tool for Measuring the Brutality of War:
Earlier this year, Hans Rosling, Professor of International Health at the Karolinska Institute, Sweden, delivered the 2008 International Health Lecture for the Academy of Medical Sciences in London, a lecture entitled "A fact-based world view". Rosling co-founded the Gapminder project (http://www.gapminder.org/): animated software that makes a multitude of quantitative datasets visible and meaningful. It was fascinating in his lecture to see health and wealth data from 166 countries move through time, making some important messages visible to a broad audience. For instance, Rosling showed the major health improvements over the last couple of decades in most countries in the world, in comparison to a small set of countries where all health development seems to have totally stagnated. This stagnant set of countries consists of most African countries and a number of conflict-affected countries elsewhere, such as Afghanistan.
Timing Precision in Population Coding of Natural Scenes in the Early Visual System:
Neurons convey information about the world in the form of trains of action potentials (spikes). These trains are highly repeatable when the same stimulus is presented multiple times, and this temporal precision across repetitions can be as fine as a few milliseconds. It is usually assumed that this time scale also corresponds to the timing precision of several neighboring neurons firing in concert. However, the relative timing of spikes emitted by different neurons in a local population is not necessarily as fine as the temporal precision across repetitions within a single neuron. In the visual system of the brain, the level of contrast in the image entering the retina can affect single-neuron temporal precision, but the effects of contrast on the neural population code are unknown. Here we show that the temporal scale of the population code entering visual cortex is on the order of 10 ms and is largely insensitive to changes in visual contrast. Since closely timed spikes are more efficient in inducing a spike in downstream cortical neurons, and since fine temporal precision is necessary in representing the more slowly varying natural environment, preserving relative spike timing at a â¼10-ms resolution may be a crucial property of the neural code entering cortex.
Venezuelan Equine Encephalitis Virus in Iquitos, Peru: Urban Transmission of a Sylvatic Strain:
Venezuelan equine encephalitis (VEE) is a mosquito-borne viral disease often causing grave illness and large outbreaks of disease in South America. In Iquitos, Peru, a city of 350,000 situated in the Amazon forest, we normally observe 10-14 VEE cases per year associated with people traveling to rural areas where strains VEE virus circulate among forest mosquitoes and rodents. In 2006 we detected a 5-fold increase in human VEE cases, and many of these patients had no travel history outside the city where they lived. In response to this outbreak, we decided to determine if potential carrier mosquitoes were present within the city and if city residents had been previously exposed to the virus. We found that mosquitoes previously shown to transmit the virus in other locations were present--in varying amounts based on location and time of year--throughout Iquitos. A large percentage of the human population (>23%) had antibodies indicating past exposure to the virus. Previous VEE infection was associated with age, occupation, mosquito exposure, and overnight travel. Our data represent evidence of transmission of a forest strain of VEE within a large urban area. Continued monitoring of this situation will shed light on mechanisms of virus emergence.
Poverty and Cataract--A Deeper Look at a Complex Issue:
In a new study published in this issue of PLoS Medicine, Hannah Kuper and colleagues sought to show an association between visual impairment from cataract and poverty in three low-income countries: Kenya, Bangladesh, and the Philippines [3]. The study had a case-control design: cases were people with visual impairment due to cataract and controls were those with no visual impairment. Since many elderly people depend on their families [4], the authors measured household wealth; to increase the validity of this difficult measurement, they used three different indicators of poverty. The researchers found that cases with visual impairment due to cataract were poorer than controls in all three countries studied. They conclude that there is a significant relationship between poverty and visual impairment from cataract.
The Role of Auxin Transport in Plant Patterning Mechanisms:
One of the fundamental questions in developmental biology is how a multicellular organism is able to create complex forms and patterns, given that every cell has the same genetic code or program. A mouse embryo separated at the two-cell stage can give rise to two identical adults, but if left together, these same two cells somehow "know" about each other and develop into a single organism. The question of how a group of equivalent cells self-organize to create a pattern was addressed by Turing [1]. Using mathematical analysis, and what is perhaps the first example of computer simulation in developmental biology, Turing showed that a pattern could emerge from a group of identical cells, all operating with identical rules. These rules involved equations for the reactions of substances, which he termed morphogens, combined with diffusion. His reaction-diffusion model of morphogenesis has since become one of the most widely used models to explain pattern formation in biological systems [2,3].
Gierer and Meinhardt [4] developed a version of Turing's model that provides intuitive insight into how reaction-diffusion works. They noticed that in order for patterning to occur, there must be some element of local activation combined with a longer-range inhibition. The local activation selects particular cells for differentiation, whereas the longer-range inhibition is required to suppress the activation of neighbors. Cast in terms of abstract but plausible substances, the model was constructed as follows.
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