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Email received September 28th 2011

Bovine TB RBCT data

Hello Mary,

I see that you have received a comment which you have added at the bottom
of your article.

 
Regarding small sample sizes, this is important because small sample size
gives large statistical error. However both the post where the recent data
has been posted and the review in the link which you give supply confidence
intervals. As sample size reduces, confidence intervals tend to increase
and the size of these intervals gives an indication of statistical error.
Figs 42a and 42b in the review at http://www.bovinetb.info/rbct.php show
these confidence intervals. Judging by their size for data taken in the
adjoining lands where perturbation was most pronounced, these intervals and
hence error are just as large, in fact significantly bigger, than the
intervals in the culling areas where beneficial effects are seen. In fact
these intervals for the most recent data are smaller than the intervals for
data which exhibited the effects of perturbation during the cull. In view
of this I am not sure what the comments regarding small sample size are
referring to. Were they referring to the sample size of data portraying the
detrimental effects of perturbation or the continuing beneficial effects
seen in the proactive areas or perhaps some completely different data?

Regarding what this is about, the only peer reviewed piece of work which I
am aware of, which has been released by the MRC, which specifically looks
at how long beneficial effects last after culling stopped is the paper
titled "The Duration of the Effects of Repeated Widespread Badger Culling
on Cattle Tuberculosis Following the Cessation of Culling" which was
published in Feb 2010. This paper stated under the section titled
"Methodology/Principal Finding" the following

<START OF EXTRACT>
We monitored cattle TB incidence in and around RBCT areas after culling
ended. We found that benefits inside culled areas declined over time, and
were no longer detectable by three years post-culling.
<END OF EXTRACT>

Judging by results which have been posted by the MRC since then, this
statement was grossly misleading. Unfortunately this is a peer-reviewed
piece of work which to many people is carrying a lot more weight and
influence than the subsequent postings which are revealing how inept this
statement was.

Regards,

David.