Saturday, May 02, 2009

punkscience: helping to understand swine flu


I read this article on swine flu and was surprised to come across the demographic parameter R0. This is something that I have regularly encountered in my work on demographics and I revel in the opportunity to explain a little straightforward maths to the pubelic: R0 is the net reproductive rate of an individual or a population.

From my thesis' scrap file:
R0 can be calculated from the equation:

R0 = V(α) . b . E(α)

Where: V(α) = Survival rate to the age of first reproduction.
b = is the product of the lifetime average rate of offspring production.
E = is the average adult life span of an individual at the age of first reproduction.

For semelparous organisms this equation can be further simplified to:

R0 = V(α) . S(α)
after Charnov (1997)

Where: V(α) = the reproductive value of an individual at the age of reproduction (b multiplied by E)

It is possible to determine several factors which influence either V(α) or S(α) and these factors have often been quantified as surrogates for fitness (eg. McDowell et al. 1999; Kashian 2004). Bearing in mind that fitness is a product of both genes and the environment in which they operate any assessment of fitness will be specific to the environment in which it is assessed (Stearns 1992).

The only problem, of course, is that a flu virus is not semelparous. In which case all of the above isn't relevant. So that's a lot clearer then. Yes.


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