Check your sources

Doug Sellman in the opinion section of today's Christchurch Press claims to have had his numbers right [not yet online]. Let's check the history here.

Here's Sellman and Connor's original press release:

Who is advising the Prime Minister on alcohol reform?

Mr Key announced today that he doesn’t believe that minimum pricing for alcohol will change the amount people drink.

“This is contrary to the scientific evidence base about alcohol pricing in general and minimum pricing in particular” said Prof Jennie Connor, medical spokeperson for Alcohol Action NZ.

“Mr Key states that what typically happens is people move down ‘the quality curve’ and still get access to alcohol. Where does this information come from? On the contrary, minimum pricing specifically targets the very cheapest alcohol options and is predicted to reduce average consumption by removing high-alcohol low-cost products from the market.”

“A recent Canadian study has shown that a 10% increase in the minimum price of alcohol reduces its consumption by 16% relative to other drinks”. [emphasis added]

“And these latest data are consistent with the scientific literature which indicates that increasing the price of alcohol has a positive impact on reducing heavy drinking”.

This is very clearly saying that there are very large price effects of increasing the cost of the lowest-priced alcohol. I had initially found the Newstalk ZB report and wondered whether she'd been misquoted, before finding the press release.

I wrote:

Connor has to have been misquoted here or the journalists left out a couple of subsequent clarifying sentences. The error is in the press release. Oh dear.

The link there is now deprecated, but the Scoop link still works.

In today's press, Sellman says that they had it right all along:

On July 3, 2012 we issued a press release recommending the government enacts a minimum price per standard drink of alcohol – to eliminate ultra-cheap drinks favoured by binge drinkers, young drinkers and heavy drinkers – and pointed to a Canadian study that showed ‘‘a 10 per cent increase in the minimum price of alcohol reduces its consumption by 16 per cent relative to other drinks’’. Our wording was based closely on the paper’s wording: “Longitudinal estimates suggest that a 10 per cent increase in the minimum price of an alcoholic beverage reduced its consumption relative to other beverages by 16.1 per cent (p0.001).”

Two days later Crampton wrote a damning critique of the press release on his personal blog, using the same arguments he later used in this Press article. However, it appears Crampton based his critique on a short Newstalk ZB news report of the press release, which quoted Jennie Connor saying, ‘‘studies show a 10 per cent increase in the minimum price of alcohol reduces consumption 16 per cent’’. Note: the reporter had cut off the words ‘‘relative to other drinks’’, which would indeed be wrong if she had said it.

Crampton’s blog piece, and his later Perspectives article, ridiculed the presumed mistake: ‘‘Can a 10 per cent increase in the minimum price of alcohol really reduce total alcohol consumption by 16 per cent?’’ he wrote. ‘‘No’’. But if he had taken the basic precaution of checking the primary source, our press release, he would have seen the words ‘‘relative to other drinks’’ and realised that we had not misquoted the Canadian study at all.

Thus Crampton’s main argument in the Press article was based on his own simple and avoidable mistake, which seems careless for a senior lecturer.

The problem isn't that the Newstalk piece left off the words "relative to other drinks" but that Sellman and Connor used that estimate as though it were relevant to average consumption and where "other drinks" would be interpreted as something other than other categories of alcoholic beverages.

Further, they might have noted that my post of 10 July quoted the press release accurately; my post of 5 July had cited the NewsTalk reporting.

If we look a bit further down the Auld paper, we see pretty clearly what Sellman and Connor had missed:

"The estimates indicate that a 10% increase in the minimum price of a given type of beverage reduced consumption of that type by about 16.1% relative to all other beverages, and a simultaneous 10% increase in the minimum prices of all types reduced total consumption by 3.4% (p<0.01 in both cases)."

Sellman and Connor were building a case in their press release that the Prime Minister was way off base in claiming that raising the minimum price would not have large effects on drinking. Whether "relative to other drinks" is included or not is irrelevant where the context suggests that "other drinks" means drinks other than alcohol.

And so I sent the letter below to the Press this morning:

Doug Sellman in Monday's Press claims to have had his numbers right all along. In his press release of 3 July, he and Jennie Connor wrote:

“Mr Key states that what typically happens is people move down ‘the quality curve’ and still get access to alcohol. Where does this information come from? On the contrary, minimum pricing specifically targets the very cheapest alcohol options and is predicted to reduce average consumption by removing high-alcohol low-cost products from the market.”

“A recent Canadian study has shown that a 10% increase in the minimum price of alcohol reduces its consumption by 16% relative to other drinks”.

The rather obvious interpretation of their release, which was highly critical of the Prime Minister's claim that minimum prices would not greatly affect consumption, was that we should expect a sixteen percent reduction in consumption of alcohol relative to other drinks were the minimum price of alcohol to rise by ten percent.

The paper on which their analysis was based does indeed have a quote that reads a lot like Sellman and Connor's. But, it refers to the effects you get if the price of one category of alcohol - like beer, wine, or spirits - rises relative to other categories of alcoholic drinks. It isn't talking about the consumption of alcohol as compared to fruit juice. This is obvious if we read the second clause of the sentence, where Auld and his coauthors write:

"The estimates indicate that a 10% increase in the minimum price of a given type of beverage reduced consumption of that type by about 16.1% relative to all other beverages, and a simultaneous 10% increase in the minimum prices of all types reduced total consumption by 3.4% (p<0.01 in both cases)."

In Monday's Press, Sellman claims not to have misquoted the Canadian study and that they had, all along, meant "relative to other drinks" to refer to other categories of alcohol. If so, it seems odd to have chosen that figure as being relevant to the argument they were building. It could be relevant if we were estimating the likely reduction in consumption of premixed "alco-pops" relative to other alcoholic beverages, but surely the total amount of alcohol consumed matters more than whether it is consumed in one type of alcoholic beverage rather than another. And, for total consumption, the 3.4% figure is the rather more relevant one.

I strongly encourage readers to read the paper on which Sellman's claims are based and to judge for themselves, rather than trusting either of us. An ungated version of it is available here: http://www.vsnews.fr/etudes/Does-Minimum-Pricing-Reduce-Alcohol-Consumption.pdf . Or, go to scholar.google.com and type "Does minimum pricing reduce alcohol consumption?" You will find that the authors there, like Sellman, favour minimum prices. I worry more about harms imposed on lower income moderate consumers of lower cost alcohol. How we weigh the tradeoff between reducing harms from heavy drinkers and reducing consumption benefits from poorer moderate drinkers is a fairly important discussion. But the case for a minimum price for alcohol ought not be based on an estimate of its effects that is roughly five times larger than that which can be supported by the evidence.