Select Committee on Agriculture Minutes of Evidence


Examination of Witnesses (Questions 20 - 39)

WEDNESDAY 15 NOVEMBER 2000

PROFESSOR JOHN BOURNE, DR CHRISTL DONNELLY AND DR ROSIE WOODROFFE

  20. This paper, she says, was referred to referees and five of the six referees agreed that points raised are fundamentally correct. "The editor concluded that I would find myself `considerably outgunned' . . .". If you are going to shoot her down in that kind of fashion, you are going to have to use more firepower than that because the essence of her argument is that the triplet study is based on a reactive strategy, that badgers are only killed after they have been associated with a herd breakdown. That is unlikely to show an overwhelming impact on TB prevalence because, as the Krebs Report points out, TB control can only be partially effective because herd rates will already have occurred, and new badgers will recolonise since only those in the immediate vicinity are going to be culled. In other words, it is crucial to be able to detect small effects, and the study—she feels—cannot do that.
  (Dr Donnelly) It is obviously a matter of degree. We have to talk about what we are talking about in terms of a small effect. Certainly we would have much less power to detect differences of, say, 5 per cent. You are very right in saying that the reactive strategy, because badgers are only culled after there is a breakdown, is probably going to produce less of an effect on incidence than the proactive, but we do not actually know that. The idea behind the proactive strategy is to remove the badgers associated with the particular breakdown. Although we would expect to have immigration occur after that, if the reactive strategy has removed the infected badgers and the badgers coming in are not infected—

  21. You do not know that.
  (Dr Donnelly) No, we do not know. That is why we are doing the trial. We have structured this to test the two different policies, and we are not prejudging it to say how they will do. However, we have examined the data that we can, and I think it might be better to talk to the editor of the journal to talk about what the referees actually said, because I certainly cannot say.

  22. If you were a referee you would not have accepted the article?
  (Professor Bourne) I think it is difficult for us because we are aware that this paper has been submitted to a number of journals, and as far as we know it has been rejected by those journals. I do not think it is one journal, I think it is a number. The fact of the matter is that this paper has not been published. Nonetheless, we have taken it, as a group, very seriously and seriously considered the contents of that paper. We believe we have robust answers to it.

  23. She is right, surely, about the weakness of the reactive strategy?
  (Professor Bourne) She may well be. There are unknowns about this. This is the whole point of doing the trial. I think the important thing for you to remember is that the direct comparison between survey only and proactive treatment is the guts of the trial. The reactive areas were included as a potential future policy option. The data we will get from the reactive aspect of the trial, in terms of scientific data with respect to answering basic questions, will be less powerful than that from the proactive area. It is primarily looking to see if it is a viable policy option.

Dr Turner

  24. In the memorandum that you submitted to us you have actually made the point in paragraph 8 that in one triplet you were unhappy with the culling effectiveness in the proactive area, and I just wondered if you could explain what effect that would have on the power. Does it delay its effectiveness, or does it mean in practice that we have lost the triplet?
  (Professor Bourne) Let us consider that in two parts. The triplet that you are referring to was one that was culled in January which ecologists recognise as being an inappropriate time of the year for badger culling. I think the data we have would support that. There were a number of reasons why we caught a low number of badgers in that particular triplet. One was, we believe, the time of the year and the relative inefficiency of the trapping. I think that was confirmed by our own audit following the trapping that we normally carry out a month after trapping has ended. The other reason, of course, could be that there had been much interference with badgers in that area through illegal activity or previous badger removal activity. Again, we are uncertain about that. We are aware that trapping efficiency was not as great there as in other triplets, and we ascribe that to the time of year.

  25. I was less interested in the reason for it as to what its effects might be.
  (Professor Bourne) Absolutely. Perhaps Christl could come in here.
  (Dr Donnelly) I suppose we also need to stress that there will be additional culling in this proactive area. The hope would be that these additional badgers—if they were not actually picked up in this initial cull in January—will be picked up subsequently. When we are actually looking at the effectiveness of the proactive or the reactive strategy, they are all looking at the actual, in practice, effectiveness. It does not actually do us a lot of good to figure out what the effectiveness would be of a perfect strategy where all badgers were instantly removed, because in making policy recommendations that will never actually happen. So what we are trying to do is get a real live test of how such a strategy would be implemented and, given its implementation, try to cull badgers but within the constraints of welfare concerns, and see what the effect of that is. That is what we are trialing. If the culling does not get every single infected badger it will not be 100 per cent effective. However, we are seeing what effect we can get putting the best of our resources and the best efforts into it.

  26. You still have not answered my question, with respect. My question was: what effect does it have on your data? I understand the point that you are making that there may be a statistical fluctuation in the effectiveness of the policy, and it may sometimes mean that you in fact modify your practices in order to make it effective, and you learn the lesson. I am really interested. Does this mean that you have lost some data for a period of time, or does it mean that the data is effective for sometime downstream in the way that the analysis takes place?
  (Dr Woodroffe) I can respond to that, if you wish. We do not yet know the effectiveness of the cull in that area, in part because the follow-up cull has not been carried out. That will help us to distinguish between the numbers of badgers culled in that area being low because of an ineffective cull or simply because there are not many badgers there. Certainly the activity on the ground in field science work did indicate rather low levels of badger activity in the area. So we certainly expected the cull there to be lower than it had been in other areas. It was lower than we expected. Subsequent culls will help us to determine the effectiveness of the first cull, in a sense, and I think the worst case scenario would be that any effects of badger culling on cattle TB would be decelerated. So the onset of any reduction you might see could be delayed, but not negated.

  27. Let us assume that it was not effective, for the moment. If it was not effective, does that mean that your data is undermined in terms of using the trial for a short period of time, or does the effect continue through—
  (Dr Woodroffe) I would argue a short period of time.

  28. It is the equivalent of losing some of your data over a short period of time in five years.
  (Dr Donnelly) It may be that we get a less effective cull in the first six months until whenever we have the follow-up cull that would actually be more effective in picking up these badgers.
  (Professor Bourne) I do not think it is a question of losing data. We accept that because we cannot cull at the most appropriate period in the year we will get variation in culling efficiency across the 10 triplets. What is important in this particular triplet is that we do not return to that same triplet at the same time of year and that we do return at a more appropriate time of the year to improve trapping efficiency.

  29. I do not think I am making myself clear, Professor. What I am really trying to understand—
  (Professor Bourne) I think I understand the question.

  30. The triplet is one of a modest number which is important to the trial. If a mistake is made, how robust is the experiment to the cull not being effective in one year or two years? Does it mean that you throw out the data?
  (Professor Bourne) I think you have put your finger on it. It is a robust trial. You are referring to the 10 trial areas as being a modest number. We believe it is not a modest number, it is an appropriate number. We expect variations between those trial areas, between triplets, so consequently the strength of the initial data will vary between those triplets, but given that we are returning to proactively cull these over a five-year period, we would expect this to even out over that five-year period.
  (Dr Donnelly) I do not think there is any reason to think that ineffective culling in a first proactive cull—if that is in fact what took place (and, as Rosie has said, we will not actually know until we get back into the area) would affect the impact of incidence in the first year.

  31. Can I ask a related question in my mind, which is the power in terms of data? There is this paper we have had which says that your calculation of your power may be wrong, and I would be interested in the consequences of that. Referring to previous Members of this Committee, when I was not on it, I think you said they totally misunderstood the role of the power calculations in your experiment. I think it is important that we do understand it now. If you prove to be wrong and the counter-view was correct, that in fact the power calculation was wrong, as the data came in would you simply be able to correct the matter by going for another year, or expanding the breadth of the experiment, or would it be a fatal flaw?
  (Professor Bourne) It would be appropriate, Christl, if you could respond to the relevance of the power calculation.
  (Dr Donnelly) Yes. In looking at the power calculation, yes, it depends on a number of factors, but the key one is the total number of breakdowns to the extent that you get violation of the assumption of independence in the breakdowns that are happening, as Fiona has noted—although it is a matter of degrees how much impact she thinks, we think and the independent auditor thinks that would have. The power could probably be increased by increasing the number of triplet years, but the power depends, in the end, on the data that is actually generated. So we will be able to look at this as time goes on. We have done our best to analyse all the data that is available retrospectively. We just do not know what the incidence will be in the underlying rate in the next five years, and we do not know what the effect of the culling will be.

  32. I have not got an answer to my question, which is if Fiona Mathews was right, in terms of the way the data started to come out, and your analysis of the data indicated that she was right, would the implication be that you then have to extend the period of the trial or would it mean that there was a fatal flaw? Would you be able to get more data simply by extending it for a year?
  (Dr Donnelly) Yes.

  33. How soon would you know that you are right and Fiona Mathews is wrong, in terms of data coming in?
  (Professor Bourne) The information I get from statisticians as Chairman of the group is that the initial power calculations should be seen as purely indicative, determining the design of the trials. The precision achieved in the trial will be determined by the data obtained totally independently of the correctness of the power calculations.

  34. I appreciate that, I understand that. I was simply asking roughly how long it will take before you will know from the data coming in whether that initial calculation of the power (and, therefore, how long this trial will have to go on for) was correct?
  (Professor Bourne) It does depend, of course, on the strength of the data we get with respect to the quantitative involvement of the badger.
  (Dr Donnelly) We would certainly want to see data from all the triplets before we actually had the best information. So it would be the end of 2002 before we would be certain of having herd test information on all herds that were enrolled in the trial. It is the time until we finish the last proactive cull, and then an additional year from that point until all the herd tests are completed.

Mr Öpik

  35. There is a high incidence of TB in Wales but it is not included in the test. Why are there no triplets in Wales?
  (Professor Bourne) I had a couple of discussions with the members of the Welsh Assembly—I have forgotten her name. The Agricultural Minister, Christine Gwyther.

  36. Sadly, she is no more.
  (Professor Bourne) The situation was that given that the wildlife unit resource was focused in Cornwall and in Aston Down in Gloucestershire, it would have been difficult for us to have used the Gloucester resource in two distant sites, one of which could well have been the western counties of Wales—in Pembrokeshire—and the other would have been in Staffordshire. Sites were selected on the basis of the previous cattle breakdowns, and we were quite keen to include new areas that have developed a high number of breakdowns in the past three years. Certainly, Staffs/Derby fitted that category. It was also useful to us in that there had been no previous badger removal operations, so it is quite different to some of the other areas that we are working in. It was also made clear to me by Christine Gwyther that while she would not welcome us with open arms to work in Wales, she would consider us doing a project there, a triplet there, if we felt it scientifically beneficial to do so. Frankly, we did not, so we are not there.

  37. Why did you not think that was useful? Do you feel that the evidence you get from elsewhere is unquestionably going to be applicable to the Welsh environment?
  (Professor Bourne) I think so. There are features of the Welsh badger removal operations which were particularly interesting to us, namely the low incidence of TB in the badger population which is recorded in Wales. As I mentioned, pragmatically and logistically, we could not work in two distant areas using the same wildlife team and stick to the timetable that we had insisted that the wildlife unit worked to. So it was a question of either working in one distant site, Staffordshire, or another distant site, Wales. Also, I am bound to say we were influenced by reports we did have of the likelihood of a large level and high level of illegal killings going on in the western parts of Wales. It was not a major influence, the major influence was the other area I have mentioned.
  (Dr Woodroffe) To reassure you, perhaps I could add that the triplets that have been selected do represent quite a wide range of habitat types and landscape types, so there should be some generality to the trials across a wide array of environmental conditions and badger densities. We hope it can be extrapolated to Wales.

  38. So you feel it can be extrapolated to Wales. I was interested to learn that we have a healthier brand of badger in Wales as well.
  (Professor Bourne) It could be infected badgers die more quickly.

  39. Moving on to the second question: you said there was about 80 per cent co-operation with the trials. How do you measure that 80 per cent? Is that the number of farmers or acreage?
  (Professor Bourne) Farmer co-operation in the trial areas has been around 80 per cent. Often it is higher but I do not think it has been very much lower. It is based upon the identification of landowners within trial areas by MAFF, who circulate each landowner by letter asking them if they will become involved in the trial. On that basis, they give permission either for surveying, surveying and culling or no co-operation at all. The non-co-operation level has been consistently around about 6 or 8 per cent. There is variation between those who will agree to culling and surveying and those who will survey only. So the figures are derived from a direct approach by MAFF staff to landowners.


 
previous page contents next page

House of Commons home page Parliament home page House of Lords home page search page enquiries index

© Parliamentary copyright 2001
Prepared 10 January 2001