July 29, 2011 • 2:07 pm

 

“Shock figures showed 6.8 billion plastic bags were handed out last year – 333million up on 2009.”

The Sun, 29 July 2011

“Perhaps owing to recessionary worries, people forgot their hessian sacks and filled up on plastic again – more than 6.8bn were used, up about 5 per cent on the previous year.”

The Guardian, 28 July 2011

There have been a number of attempts in the last decade to significantly reduce the number of plastic bags used by consumers in supermarkets. Campaigners claim that they cause substantial damage to the environment and have argued for legislation on plastic bag usage.

Reports that have surfaced in the last few days suggest that despite a trend of falling plastic bag use in the last five years, last year saw a reversal of this process.

But what do the figures show?

Analysis

Yesterday, WRAP (Waste & Resources Action Programme) published a press release on supermarket-based carrier bag use. The report sets out the data on the number of carrier bags used in British supermarkets in the last two years and in 2006.

Both the Guardian and The Sun state that 6.8 billion plastic bags were used in supermarkets last year.

However, a closer inspection of the figures shows that the figure of 6.8 billion actually refers to the total number of bags used in supermarkets last year which includes ‘single-use, bags-for-life and reusable bags such as those made from cotton and jute’.

Therefore not all of the 6.8 billion bags used were plastic single use bags; some were re-usable plastic and cotton bags. The report does also provide the figures which only refer to single use bags which show that 6.4 billion of these bags were used last year.

Whilst the papers are correct in reporting that the number of plastic bags has increased on last year, it has increased from 6.1 billion to 6.4 rather than 6.5 billion to 6.8- which is the total bag use increase.

Whilst this confusion of data may not seem to be all that significant, what the correct figures actually suggest is that whilst both the total number of all bags and total plastic bags have increased on last year, plastic bags as a percentage of all bags has decreased very slightly.

Both reports make reference to the fact that since 2006, usage of carrier bags in general has fallen by 40 per cent.

Another potential problem with the conclusions drawn from the figures is of the percentage rise in plastic bag use. This comes from looking at plastic bag use from June 2009-May 2010 and January 2010-December 2010. So the five per cent rise is not based on a comparison between two separate years, but two years that have a five month overlap.

It is still possible to say that usage has risen between the two periods. This is because both the 6.1 billion and 6.4 billion numbers will both contain the bags used in the five months January to May 2010. 

Bag usage in January to May 2010 will be the same in both sets of figures, so it follows that in the months which don’t overlap – June-December 2009 and June-December 2010 – the latter period saw 0.3 billion more bags used.

However we do not know what the 0.3 billion rise would be as a percentage of change in plastic bag use without a direct year on year comparison.

The Guardian makes reference to this and explains that ‘plastic bag data is difficult to compare over the past five years, because of changes in the way the statistics are collected’.

However the Sun makes no reference of the way in which the data was collected, suggesting the figures from the previous year were from the year 2009, rather than 2009/10.

The Sun also included figures from the report which stated that each person used, on average, 8.6 single-use bags per month in 2009/10.

However the report also stipulates that the data is based on figures from all the major supermarkets except Morrisons, who have only provided data since 2010 and have therefore been excluded to maintain continuity of reporting.

Morrisons claim that their market share at the beginning of 2011 was 12.8 per cent and therefore creating data on the average number of bags used per person without including Morrsions customers potentially ignores a proportion of the population.

Other publications also picked up on the story today; the Daily Mail reported the correct figures relating to single-use bags but made no mention of the potential problem with the overlap of data.

Conclusion

Whilst the newspapers were correct in reporting that, based on the figures, there has been a small increase in the number of plastic bags being used in supermarkets after a significant fall since 2006, both the Guardian and the Sun seemed to confuse the figures.

The change in the way in which data was collected between in 2010 and the previous year means that it is difficult to know what the true percentage change in the number of plastic bags used has been. 

 

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