|"It's only a model"|
There's an interesting article in the European Journal of Public Health in which academics, politicians, civil servants, campaigners and industry bods speak anonymously about minimum pricing. Specifically, they talk about the Sheffield minimum pricing model and its role in policy-making. It's clear that many of them realise that the Sheffield 'evidence' is only a model and that models are less reliable than traditional (ie. hard) evidence. These doubts were not always communicated to the public (to put it mildly) and campaigners/academics were torn between being frank about the state of the evidence and wanting to persuade politicians to take the policy forward.
Many interviewees expressed the view that modelling, while helpful, was imperfect and subordinate to other forms of academic knowledge. There, therefore, appears to be an important distinction made between what might be considered more conventional forms of evidence (such as trials and evaluations) from the type of econometric modelling exemplified by the Sheffield study. The somewhat ambiguous status of modelling studies led to active discussion among some actors more familiar with more frequently used forms of public health evidence, such as epidemiological studies and evaluations. On some occasions, this led to a tension for public health professionals between maintaining a commitment to being ‘evidence-based’ (as underpinned by studies of effectiveness of public health interventions) and their responsibility as public health advocates.
Do read the whole article if you have time. If not, here's a few choice quotes...
Academic: When politicians and journalists ask you for your opinions, ‘well maybe they really want to hear my opinions’ and I did get a bit carried away and felt that I had been unfaithful to my scientific training because I suddenly felt that I really did believe that minimum unit price was going to be a good thing. Whereas to be honest, we don’t know. We don’t know. We’ve got models. Sheffield modelling etc, all the taxation stuff but we don’t know. And we don’t know what’s gonna happen to the very heavy, heavily dependent drinkers. We actually don’t know and there may be some pluses and minuses.Academic: (Laughs). Well I like the little platitude of ‘do you believe the weather forecast? That’s modelling’. You take data, you use it, you try to make your best guess based on the relationships and trends you can see. You try to make the best predictions from that. I’m in sympathy with people who say ‘it’s just modelling’. And therefore I think the only answer can come from running the experiment and the Scottish government has been very courageous to run the experiment.Academic: I do sometimes think that perhaps a little too much certainty is place on the results of the modelling. So when you look at a lot of the discourse from supporters of minimum pricing in Scotland where they talk about the policy leading to X number of saved lives in year one or fewer admissions or whatever, you know, it’s worth kind of bearing in mind that there’s a huge amount of uncertainty around those estimates. I don’t expect ministers to say you know 40 fewer deaths plus or minus 35 but it would be nice to have some acknowledgement that this is based on model estimates without it coming over as this will definitely happen because I think it leaves you open to possible criticism if it doesn’t happen.
My own frustration with the minimum pricing debate was never about the Sheffield group building a model—which is a perfectly valid thing to do, whatever its flaws—but with the almost religious faith that campaigners, politicians and the media put in it. Its estimates were cited with ludicrous precision (eg. "a minimum unit price of alcohol of 50p will annually save 3,393 lives and reduce hospital admissions by 97,900") as if they were proven historical facts—as if there were no doubt. It's a relief to know that behind the scenes, there was a good deal of healthy scepticism.