BACKGROUND AND AIMS Buying smaller-sized alcohol products can reduce alcohol consumption, but larger products have better value for money, which presents a barrier to switching. We tested whether proportional pricing prompts drinkers to buy smaller alcohol products and reduce alcohol purchasing.

DESIGN, SETTING AND PARTICIPANTS This study was an online experiment set in the United Kingdom, using hypothetical shopping tasks in which participants purchased different-sized products presented under proportional pricing (i.e. constant price per litre throughout all sizes of the same product) or standard pricing conditions. Study 1 (comprising n = 210 participants) was a mixed experiment with pricing condition (proportional pricing, standard pricing; within-subjects) and drink type (lager, red wine, vodka; between-subjects) as manipulated factors. Study 2 (comprising n = 90 participants) was a within-subjects experiment with pricing condition (proportional pricing, standard pricing) and multi-pack type (size difference-only, quantity-difference only, size and quantity difference) as manipulated factors. Participants were UK adult alcohol consumers.

MEASUREMENTS We measured outcome variables, including alcohol purchasing (UK units) and proportion of alcohol purchased from smaller products.

FINDINGS Proportional pricing consistently increased the proportion of alcohol purchased from smaller products [study 1: B = 10.82, 95% confidence interval (CI) = 8.72-12.92; study 2: B = 11.64, 95% CI = 3.50-19.77], indicating a switch to smaller products. However, this did not consistently reduce the total amount of alcohol purchased among drink and product types: proportional pricing reduced the total units purchased from lager multi-packs containing more rather than fewer products (B = -2.56, 95% CI = -4.82 to -0.30), but not from other types of lager multi-packs or single lager products. Proportional pricing also reduced vodka purchasing (B = -3.30, 95% CI = -5.21 to -1.40), but the effect of proportional pricing on wine purchasing was moderated by hazardous drinking (B = -0.11, 95% CI = -0.17 to -0.05).

CONCLUSIONS Alcohol sales policies that require proportional pricing may reduce alcohol purchasing.