Potato logic: News media repeat zombie statistics on food wastage
Major UK news outlets gleefully announced today that 30% of the UK vegetable crop is ‘never harvested’ and half of the world’s food is ‘thrown away’. A major initiative by Waitrose to reduce food waste has been strangely inverted by statistical spin-doctors and journalists into a supermarket bashing story! Real levels of harvesting wastage are probably less than 10%, and difficult to avoid.
This blog reveals how respected news organisations across the UK have fallen for the oldest trick in the book. In today’s news hungry environment, when you need to get noticed, the best way is to get some spurious stats and then exaggerate, exaggerate, exaggerate. And this is what the UK Institute of Mechanical Engineers (IMechE) did today.
You have to hand it to Erica Herrero-Martinez at the IMechE press office – she got the media to swallow the story hook, line and sinker!
This blog is about using evidence and facts to determine government policy and execute effective change initiatives. I am a sceptic. I am not a negative thinker. I just do not accept statements as facts without supporting evidence. We must be scientists – we should not accept the authority of an author at face value…
Let’s look at the story…
A headline news article on the front page of the BBC news website said:
“Half of all food is thrown away … (and) up to 30% of vegetables in the UK were not harvested because of their physical appearance.”
Source: www.bbc.co.uk/news (accessed at January 10, 2013, 09:10am)
The source is a report published today by the UK Institute of Mechanical Engineers.
“Half” is not the same as “Up to half”
Headlines are typically not written by the journalist who wrote the article. A sub-editor will scan the journalist’s text. You will often see inconsistencies and exaggerations between a headline and the detail of the text – and this case is no different.
The text in the body of the BBC article actually says:
“As much as half of the world’s food, amounting to two billion tonnes worth, ends up being thrown away.”
OK – so it is “as much as half” not “half”. We don’t know how much less than 50%.
49% perhaps? One percent perhaps?
Are “30%” of UK vegetables never harvested?
No. Let’s go and check the detailed report. It does indeed claim that:
“up to 30% of the UK vegetable crop is never harvested.”
Source: Global Food. Waste not, want not. London: Inst. of Mechanical Eng., 2013, p.18
Wow. That sounds very worrying. Let’s look at the evidence on which the report’s (anonymous) author is basing this disturbing statement.
The source given on page 31 is:
“War on Waste, Solanum in collaboration with Waitrose”
Well, this is a strange reference. There is no date or indication of the author, format of the report, its location or availability. This aroused my suspicions…
Digging around the Internet for potato stats
In fact, I had to do quite a lot of searching to check out this ‘fact’.
The name of the source is interesting. Remember what the subject of today’s blog is? Yes – the humble potato, solanum tuberosum.
It turns out that Simon Bowen (an expert potato nematologist)1, the technical director of an organisation called Solanum UK (which is part of the Produce World Group2) gave a talk at the World Potato Congress in Edinburgh in May 2012.3
Farmer’s Guardian online reported on Simon’s talk as follows:
“Simon Bowen, technical director at Solanum UK and Alan Wilson, technical manager for agronomy at Waitrose, discussed their joint ‘War on Waste’ project. … The standards of the supermarket and its growers are among the best in the country … in 2008 (the) average loss from field to supermarket shelf (was) 42 per cent, although some of those rejected potatoes would be sold to secondary lower value markets. A strategic approach identifying and addressing problems had since been implemented. Its aim was to reduce waste to 33 per cent by 2011. Dr Bowen said, that in a difficult year, this target was missed by just 3 per cent.”
Source: Farmer’s Guardian Website, June 6, 2012
So, Waitrose has reduced its waste to 33% plus 3% = 36%. It looks like the report’s authors made an arithmetical error in coming to a 30% figure by subtracting 3% instead…
OK – so are 36% of potatoes in the UK are not harvested by Waitrose suppliers?
Farmer’s Guardian (which I am coming to respect more and more as I delve into these stats!) provides a breakdown of the survey’s findings:
(The more nerdy of you out there may have fired up Excel to check my arithmetic, and may be wondering why the above numbers don’t add to 42% – this is, I shall assume, simply due to presentational rounding errors.5)
So only 12% + 1% = 13% appear to be ‘lost’ by grading losses or supermarket quality control…
Wait a minute!
Of the 12%:
“some … would be sold to secondary lower value markets“.
So the true level of loss due to what a commentator on Radio 4 today called ‘wonky vegetables’4 is less than 13%. Presumably what remains are tubers that are so misshapen that they cannot be readily prepared for consumption…
It gets worse…
This is a survey for Waitrose, who (as Farmer’s Guardian correctly states) have probably the most exacting of quality standards of any major UK supermarket. I would expect that more ‘down-scale’ supermarkets would have lower scales of loss.
Let’s check out the dates…
These figures are from 2008! Waitrose (that evil, capitalist supermarket) has since instituted programme called ‘War on Waste’ which has resulted in potato losses reducing from 42% to just 36%. The 13% breakdown is more than four years old. We do not have an updated current breakdown of the harvested food that is ‘thrown away’, but it is somewhere between 7% and 13%.
Four years ago, a survey of twenty suppliers of potatoes showed that less than 13% were not accepted by an upmarket UK supermarket. Some of this 13% were sold elsewhere. Since then, a project initiated by the supermarket has reduced overall wastage by 6%.
This statement has been expanded and extrapolated out at each step of the process from Dr. Simon Bowen’s original verbal report into the news release today that 30% of UK vegetables remain unharvested. The authors have extrapolated various other statistics which have resulted in a misstatement by the news media that half of all food is thrown away.
I fully expect the 50% and 30% numbers to now become zombie statistics,6 being repeated for many years to come as unassailable facts.
Welcome to the modern world of statistical spin-doctors and journalism!
3 WPC 2012
4 BBC Radio 4 News January 10, 2013 11:00am
5 See nerdy paper here
© Brian Wernham 2013 CC BY-NC-ND