The effect of proportional pricing on alcohol purchasing in two online experiments

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.