Impact of tax and subsidy framed messages on high- and lower-sugar beverages sold in vending machines: a randomized crossover trial

Abstract

ObjectiveFraming of fiscal incentives has been suggested to be important in influencing purchase decisions. We aimed to examine the effect of framing a modest price difference between high- and lower-sugar beverages as a tax or a subsidy respectively, using messages placed on vending machines to influence beverage purchases.Design/settingThis is an 11-week randomized crossover trial conducted between August and November 2015, with a two-week run-in period before intervention, targeted at students, staff and faculty of a university campus in Singapore. Twenty-one beverage vending machines were used to implement the intervention involving ‘tax message’, ‘subsidy message’ and ‘no message (control)’. The former two messages suggest ‘a tax for high sugar beverages’ or ‘a subsidy for lower sugar beverages’ respectively. Prices of the beverages offered were fixed at baseline and remained the same in all three experimental conditions: lower-sugar beverage options were priced ~ 10% lower than the corresponding high-sugar option. The machines were randomized to one of the 6 sequences of intervention. Each message intervention period was 3 weeks. The effect of messages was assessed by comparing average weekly units of beverages sold between interventions using mixed effects model.ResultsThe average weekly units of high and lower-sugar beverages sold per vending machine were 115 and 98 respectively in the control condition. The percentage of high-sugar beverages sold was 54% in the control, 53% in the tax, and 54% in the subsidy message condition. There was no difference in the weekly units of high-sugar beverages sold for the tax message (− 2, 95% CI -8 to 5, p = 0.61) or the subsidy message (0, 95% CI -10 to 10, p = 0.96) conditions as compared with the control condition. Similarly, there was no difference in the weekly units of lower-sugar beverages sold for the tax message (4, 95% CI -4 to 13, p = 0.32) or the subsidy message (7, 95% CI -4 to 18, p = 0.18) conditions as compared with the control condition.ConclusionsThe use of tax and subsidy messages to highlight modest price differences did not substantially reduce high-sugar beverage sales in vending machines on an Asian university campus.Electronic supplementary materialThe online version of this article (10.1186/s12966-018-0711-3) contains supplementary material, which is available to authorized users.

Effectiveness of Nutrition Interventions in Vending Machines to Encourage the Purchase and Consumption of Healthier Food and Drinks in the University Setting: A Systematic Review

“…The types of intervention strategies included promotion of healthier food and drink choices (n = 11, 85%) [13,14,[17][18][19][20][21][22][23][24][25], increasing the availability of healthier food and drinks within vending machines (n = 8, 62%) [13,14,[22][23][24][25][26][27], price alterations (n = 4, 31%) [13,14,20,24], and modifying product placement within vending machines (n = 2, 15%) [14,23]. Interventions in seven studies involved more than one of these strategies, with three studies using two strategies [20,22,25], three studies using three strategies [13,23,24], and one study using four strategies [14]. The most common combinations of strategies were increasing the availability and promotion of healthier food and/or drink choices [22,25] and increasing the availability and promotion of healthier food and/or drink choices and price alterations [13,24], used in two studies each.…”

“…Interventions in seven studies involved more than one of these strategies, with three studies using two strategies [20,22,25], three studies using three strategies [13,23,24], and one study using four strategies [14]. The most common combinations of strategies were increasing the availability and promotion of healthier food and/or drink choices [22,25] and increasing the availability and promotion of healthier food and/or drink choices and price alterations [13,24], used in two studies each. The outcome measures included purchases/sales from vending machines in all except one study (n = 12, 92%) [13,14,[17][18][19][20][21][22][23][24][25][26]28] (Table 2).…”

“…The most common combinations of strategies were increasing the availability and promotion of healthier food and/or drink choices [22,25] and increasing the availability and promotion of healthier food and/or drink choices and price alterations [13,24], used in two studies each. The outcome measures included purchases/sales from vending machines in all except one study (n = 12, 92%) [13,14,[17][18][19][20][21][22][23][24][25][26]28] (Table 2). Two studies (15%) also measured the acceptability of/satisfaction with the intervention [22,26], and one study (8%) also measured dietary behavior change [22].…”

“…In seven studies (3 RCTs, 3 pre-post tests, 1 non-randomized controlled trial), interventions involved a combination of two or more strategies [13,14,20,[22][23][24][25]. Of these, four studies (57%) reported positive change in outcomes [13,14,20,23].…”

“…In two RCT studies, interventions involved increasing the availability and promotion of healthier food and/or drink choices and price alterations [13,24]. The study by Hua et al involved a 2 × 2 × 2 factorial design, with factors including increased availability of healthier products (100% of snack/75% of beverage options meeting healthy guidelines), price reductions (25% price reduction on snack items meeting healthy guidelines/$1 water) and promotional signage (promoting nutrition information of items meeting healthy guidelines and/or price reductions) [13].…”