Since there is going to be a certain amount of numbers in this piece, I thought I’d start by making one thing very clear. When I use a number to support my argument, it is robust, accurate and completely reliable. When you use a number to refute my point it is a statistic and we all know the one about ‘lies, damn lies and statistics’.
It seems to me that it is this positioning that makes it so difficult for people to accept evidence, when it truly is, leading to the same subjects going round and round.
We are now three days into the British Horse Society’s Ragwort Awareness Week (RAW) and the survey has been available online since Monday. It is supposed to be a way of measuring the prevalence of Jacobaea vulgaris (syn. Senecio jacobaea), common ragwort.
I’ve written about this several times before. The most recent piece was last Wednesday but if you follow the link, above, to the plant page you’ll get a full list of previous blog entries.
I’ll try not to repeat too much of what I’ve written before but, today, I want to concentrate on how a number becomes a statistic. The BHS press release announcing RAW says that its survey found that 75% of respondents reported seeing animals grazing in fields with the plant present or nearby. That’s fine, it is a perfectly easy to calculate number, assuming you have access to the full survey results as the BHS does.
The problem is that the BHS tries to present that number as evidence of the spread of common ragwort and hopes to use it to build its campaign for further action against the plant. And that is when it becomes a statistic.
The introduction to the RAW survey1 says;
‘if you spot any ragwort (emphasis added) close to or in fields grazed by horses, cattle or sheep during Ragwort Awareness Week (22 - 29 July) do take a couple of minutes to report it to us using this survey.’
It specifically asks you to complete the survey only if you have seen what you think was ragwort. If people completed the survey as instructed, then 100% of respondents would have seen a yellow plant in or near fields with grazing animals. That only 75% did doesn’t actually mean anything, because the survey doesn’t mean anything, but, from the BHS’s spinpoint, it means ragwort is not the problem the BHS is trying to make it out to be.
We know that the BHS is responsible for turning 75% from a number into a statistic because it appears on its own website. Other times, of course, the media is doing the lying in order to make a story more dramatic or more immediate.
For once, I’m not going to provide any links for what follows. This is because I did not say, when making my enquiries, that I planned to publish any information supplied and I feel it would be impolite to go back now and seek it. In any event, the general point is what matters.
I saw a local newspaper report about RAW including quotes from a local equestrian facility. These said that ragwort was a serious problem requiring annual control activities and that, ‘last year’ a horse at the facility had died from liver failure resulting from the ingestion of ragwort.
I am genuinely interested to hear about specific cases of liver failure in horses especially if it can be attributed to animals grazing on living plants. For that reason, I tracked down the centre concerned and ask for more information about the case. The reply I received said that they were certain that the animal had not ingested ragwort on their property but had displayed symptoms of liver failure shortly after arriving from elsewhere. In other words, they did not know whether the animal had grazed on Jacobaea vulgaris or been fed dead plant material in poorly produced conserved forage whilst in someone else’s care.
More interestingly, they also said that this incident happened ‘a few years’ ago and not last year as claimed by the newspaper.
They went on to volunteer the information that the business had been operating for 27 years, that ragwort had needed to be removed every one of those years and that they had only lost two horses to liver disease in all that time. They were adamant that neither animal had ingested living ragwort whilst in their care.
1.Ragwort Awareness Week Survey 2012 Survey Monkey