Select Committee on Environment, Food and Rural Affairs Minutes of Evidence


Memorandum submitted by Professor Denis Mollison

COMMENTS ON THE CHIEF SCIENTIFIC ADVISER'S REPORT, "BOVINE TB IN CATTLE AND BADGERS", PUBLISHED ON 22 OCTOBER 2007

  I write as the Independent Statistical Auditor of Defra's Randomised Badger Culling Trial (RBCT).[3]

  The Final Report of the Independent Scientific Group (ISG) on the RBCT was painstaking, expert and balanced, and I commended it to Ministers as an exemplar of how to bring high quality science into public decision-making. The ISG's main modelling and statistical analyses have been published in the highest quality peer-reviewed journals, such as Nature and the Proceedings of the National Academy of Science.

  In stark contrast, the Chief Scientific Adviser's comments published yesterday, as a report Bovine TB in cattle and badgers, would not have passed my audit. It is unbalanced and inexpert.

  First, one has to question why he had to assemble an "expert group" to comment on the ISG's Report at all, when its analysis was of such quality and its conclusions so clear. It undermines the concept of independent scientific advice when it is filtered in this way.

  Next, his report is mainly concerned with detailed discussion of complex statistical modelling and data analysis issues. Yet neither he nor any of his "expert" group have expertise in this area comparable with Professors Cox and Donnelly of the ISG.[4]

  One consistent theme of Sir David King's report is its attempt to play down or dismiss the ISG's findings of detrimental effects near the edge of culled areas. These range from picking apart statistical fine details in a textbook example of special pleading (para. 43), to their wishful thinking that disruption (under a continuing culling programme) may be transient (para. 37). They even suggest there may still be a role for the reactive strategy (para 50), contrary to the conclusions of the ISG accepted by Ministers in 2003.

  Their epidemiological analysis is muddled in its discussion of the basic concept of R0 (paras 9-11 and Annex 2); and on a substantive point, the results of Cox et al indicated an R0 of about 1.1 not for cattle-to-cattle but for the whole cattle-badger system, suggesting that cattle controls on their own might well be sufficient to reduce this overall transmission parameter R0 to a value less than 1, and thus bring the disease into decline.

  Nor do they discuss the economics: the ISG concluded that the proactive strategy, if carried out over large enough areas (of the order of 300 sq km), should have a beneficial effect, but estimated this not to be cost-effective.

  Finally, the language used is not always careful. For example, "Strong action needs to be taken now" (para 4) sounds good, but if this refers to badger culling, the ISG report makes clear that in many circumstances "strong action" would be likely to make matters worse.

October 2007




3   My final audit report can be found at http://www.defra.gov.uk/animalh/tb/isg/pdf/statsaudit_rpt0607.pdf Back

4   Professor Sir David Cox is of particular international distinction, including for his many books and papers on statistical modelling, and for his integrity and the care and balance he brings to any argument. He is a past President of the International Statistical Institute (http://www.stats.ox.ac.uk/people/academic_staff/david_cox). Professor Christl Donnelly is internationally recognised for her experience and abilities in the detailed statistical analysis of infectious disease data, and is also most careful and balanced in presenting her conclusions (http://www1.imperial.ac.uk/medicine/people/c.donnelly/). Back


 
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