Addiction Research and Theory

December 2009; 17(6): 580–582

Commentary

The price of alcohol and the value of the ceteris paribus

assumption

JIM MCCAMBRIDGE1 & KYPROS KYPRI2

1Department of Public Health and Policy, Centre for Research on Drugs and Health Behaviour,

London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK and2Centre for Clinical Epidemiology and Biostatistics, School of Medicine and Public Health,

University of Newcastle, Australia

(Received and accepted 8 June 2009)

There can be few topics in addiction sciences with so much current importance to public

policy as the effects of price on levels of alcohol consumption and harms. The actions and

apparent inactions of policy makers reflect and symbolically reinforce the position of alcohol

within society. Unsurprisingly, there are extensive industry strategies to avoid or minimise

policy action on price in pursuit of business interests. The strength of the research evidence

on price is thus a key point of conflict between the largely nationally based interests of public

health and social protection on one hand, and the economic interests of multi-national

corporations on the other.

In this context, the efforts of Room et al. (2009) are remarkable. Study of the effects of

various price reductions and availability extensions in Denmark, Sweden and Finland

appeared to contradict the research evidence by having little obvious impact on

consumption, (Makela et al. 2008) and these data stimulated the present article. These

uncomfortable findings have been published and grappled with, rather than buried or

ignored. The international leaders of the alcohol and public health field thus demonstrate

well how science should be practised.

As this article was conceived as part of an attempt to understand the unexpected prior

findings, some observations on the original study and the more general research literature on

price are necessary, before addressing this article directly. Stockwell (2008) has already

Correspondence: Jim McCambridge, Department of Public Health & Policy, London School of Hygiene & Tropical Medicine,

Centre for Research on Drugs & Health Behaviour, Keppel Street, London WC1E 7HT, UK. Tel: þ44 (0)20 7927 2945. Fax: þ44

(0)20 7580 4524. E-mail: Jim.McCambridge@lshtm.ac.uk

ISSN 1606-6359 print/ISSN 1476-7392 online � 2009 Informa UK Ltd.

DOI: 10.3109/16066350903145106

Add

ict R

es T

heor

y D

ownl

oade

d fr

om in

form

ahea

lthca

re.c

om b

y T

he U

nive

rsity

of

Man

ches

ter

on 1

1/01

/14

For

pers

onal

use

onl

y.

covered study design and methodological problems that are important to the interpretation

of the Nordic study. Briefly, it is necessary to sharpen research instruments for more forensic

studies which minimise bias and confounding in cohort studies reliant upon self-reported

behavioural data.

Quasi-experimental comparisons can be valuable but are not straightforward to do.

Problematic reactivity to research assessments may well occur extensively in studies of

drinking behaviour, and this phenomenon may have been better recognised in brief

interventions trials than elsewhere. Unexpected behaviour change in control groups occurs

widely, is complex and warrants research scrutiny in its own right (Jenkins et al. 2009).

The possible value of these types of studies is that they have greater potential to evaluate

impacts upon population sub-groups, and permit examination of hypothesised mediating

variables, than do studies based on sales data for consumption, or morbidity or mortality

data for harm outcomes (Kypri et al. 2009).

Nothing in the remarks which follow should give succour to industry attempts to deny and

diminish the existing evidence base, or be interpreted to undermine the research community

consensus that sufficiently strong evidence for actions on price to reduce harm should be

implemented by policy makers. The literature on price is large and the coherence of

findings means that it would be pretty astonishing if price increases did not generally lead

to reductions in consumption and harms. The model proposed by Room et al. (2009)

appropriately identifies constraints upon these effects, with implications for the size of effects

to be expected in any given situation in which price controls are applied.

Notwithstanding the sophisticated meta-analyses of Wagenaar et al. (2009), uncertainties

stemming from the reliability of the data from the primary studies lead one to question the

magnitude of the effects that can be expected when policy makers do use taxation to alter

price. When individual price elasticities are aggregated meta-analytically, there can be little

confidence that summary measures will be meaningful if there is much bias in the primary

study estimates. In addition to the available reviews of this literature, one wonders what

would be found by a systematic review of price and price changes which was more restrictive

of inclusion by study design.

It is noteworthy that estimates of the effects of price changes are consistently higher

in aggregate as opposed to individual level studies. Wagenaar et al. (2009) dismiss the

differential in the size of the pooled effects of aggregate and individual levels as being

a methodological artefact. Yet, it may be possible that when the statistical artefact

is controlled there remains a difference in the size of the effects, which is a true difference:

The size of the effects on aggregate outcomes may be genuinely larger than those that can be

captured from individual level self-reported behavioural outcomes, partly due to differences

in the nature of the outcomes and partly due to differences in the reliability of their

ascertainment. Thus sales data may produce more valid outcome data than do population

surveys. For example, in Finland there appeared to be no consumption or harm increase

following a large price reduction identified in surveys, whilst there was an approximate 10%

increase in sales data, and a 17% increase in alcohol-involved sudden deaths, all in 2004

(Koski et al. 2007; Mustonen et al. 2007; Makela et al. 2008). Perhaps, we under-estimate

the value of sales data and other aggregate outcomes for population-level hypotheses (Gmel

et al. 2004), a tendency this article will help remedy.

These thoughts have principally been directed towards the internal validity of inferences

drawn from data on price, whilst the paper by Room et al. is more concerned with external

validity and the circumstances in which estimates of effects in research studies may be

reliably applied by policy makers. This article provides rich reflections on the social forces

which shape these circumstances. Saturation is revealed to be a crude description with little

The price of alcohol and the value of the ceteris paribus assumption 581

Add

ict R

es T

heor

y D

ownl

oade

d fr

om in

form

ahea

lthca

re.c

om b

y T

he U

nive

rsity

of

Man

ches

ter

on 1

1/01

/14

For

pers

onal

use

onl

y.

or no explanatory power. The need to situate policy decisions within long-term cultural and

historical context is clear.

The simple model provides a conceptual map of the social context for the policy maker,

as well as for the researcher. Whilst the simplicity of the model is deeply attractive, and

presumably this is a strategic choice made by the authors with policy makers in mind, it is

difficult to avoid wondering what a fuller version would look like. This might do justice to

the range and subtlety of the social forces identified in the text, and may be more useful

for active hypothesis generation by researchers. Ceteris paribus is a simplifying assumption

that may be useful for study purposes, even though it never actually applies. There are

always a multitude of forces acting upon the variables of interest, sometimes subtle and

unmeasurable. Their aggregate effects, however, may be powerful. This report and the

simple model proposed captures well both the complexity and profundity of these social

forces. This article has interesting and important implications for evaluations of the strength

of the evidence on price and for modelling policy changes, indicating the need to incorporate

the types of variables identified here in future studies.

Declaration of interest: The authors report no conflicts of interest. The authors alone are

responsible for the content and writing of this article.

References

Gmel G, Rehm J, Room R. 2004. Contrasting individual level and aggregate level studies in alcohol research?

Combining them is the answer! Addiction Research and Theory 12:1–10.

Jenkins RJ, Mcalaney J, Mccambridge J. 2009. Change over time in alcohol consumption in control groups in brief

intervention studies: Systematic review and meta-regression study. Drug and Alcohol Dependence 100:107–114.

Koski A, Siren R, Vuori E, Poikolainen K. 2007. Alcohol tax cuts and increase in alcohol-positive sudden deaths:

A time-series intervention analysis. Addiction 102:362–368.

Kypri K, Davie G, Langley J, Voas R, Begg D. 2009. The utility of routinely collected data in evaluating important

policy changes: The New Zealand alcohol purchasing age limit. American Journal of Public Health

99(7):1212–1215.

Makela P, Bloomfield K, Gustafsson NK, Huhtanen P, Room R. 2008. Changes in volume of drinking after

changes in alcohol taxes and travellers’ allowances: Results from a panel study. Addiction 103:181–191.

Mustonen H, Makela P, Huhtanen P. 2007. People are buying and importing more alcohol than ever before. Where

is it all going? Drugs: Education, Prevention and Policy 14:513–527.

Room R, Osterberg E, Ramstedt M, Rehm J. 2009. Explaining change and stasis in alcohol consumption.

Addiction Research and Theory 17(6):562–576.

Stockwell T. 2008. A hard natural experiment to fathom: A testament to the increasing difficulty of conducting

reliable surveys? Addiction 103:192–193.

Wagenaar AC, Salois MJ, Komro KA. 2009. Effects of beverage alcohol price and tax levels on drinking: A meta-

analysis of 1003 estimates from 112 studies. Addiction 104:179–190.

582 J. McCambridge & K. Kypri

Add

ict R

es T

heor

y D

ownl

oade

d fr

om in

form

ahea

lthca

re.c

om b

y T

he U

nive

rsity

of

Man

ches

ter

on 1

1/01

/14

For

pers

onal

use

onl

y.