Tuesday, September 27, 2011

RBCT Update

Although the operatives of the Badger Dispersal Trial RBCT ended their 8 night forays (if they arrived at all) and chopped up the cage traps in 2005/06, data collection from this exercise in prevarication, continues.

We posted the first offerings from Prof. Donnelly's mathematical abacus in 2008. This was followed by a further tranche of number crunched advantages (and cost disadvantages) in 2010 which we posted here.

And last week, the modelling machinery clanked into action again with the following observations on the longer term effects of this most peculiar option of 'controlling' bTB in badgers. The paper makes the following observations:
In the time period from one year after the last proactive cull to 28 August 2011 (the post-trial period), the incidence of confirmed breakdowns in the proactive culling trial areas was 28.0% lower (95% CI: 15.0% to 39.1% lower) than in survey-only areas, and on lands up to 2km outside proactive trial areas was 4.1% lower (95% CI: 25.7% lower to 23.7% higher) than outside survey-only areas.
and continues;
Exploratory analyses stratified by 6-month periods (Table 1) are consistent with an ongoing, but diminishing (test for temporal trend p=0.008), benefit of proactive culling continuing through the latest 6-month period analysed (55 to 60 months post-trial).
The paper also observes that "the effects observed outside trial areas remained consistent with no ongoing effects of proactive culling in these areas."

Stating that their
"post-trial results must, of course, be considered in the context of the smaller reduction seen inside proactive trial areas and the increased incidence seen outside proactive trial areas in the period from the end of the initial proactive cull until one year after the last proactive cull in each triplet."
..... we can at least see where the current 'benefit' of culling modelled at a modest 16 per cent only, has come from.

But in the real world, well away from the square root of stupid, one would assume that the response to culling an infected GROUP of badgers would be somewhat different from picking off the scent markers one at a time during 8 nights annually, with time out for FMD and during hibernation periods, over six years. Thus the resulting drop in cattle TB would be more marked, as in Thornbury where a 100 percent drop in cattle TB was observed over a decade later, and more recently the RoI strategy where a more thorough and ongoing clearance is having marked and beneficial effect on cattle TB incidence.

A full analysis with graphs, of all this modelling post Badger Dispersal Trial RBCT can be seen here.

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