Plastic bag purchases dropped after Armenian grocery shoppers received a letter and SMS reminders on plastic’s harmful effects.
What unsustainable behaviour needs to change:
In Armenia, plastic bags are widely available and commonly distributed at grocery checkouts, contributing to high usage rates and adding to local waste streams. Many shoppers rely on plastic bags out of habit and convenience.
This persistence reflects familiar cognitive biases—such as ‘status quo bias’ and ‘present bias’—that make entrenched behaviours difficult to shift. While bans and levies can reduce plastic use, they’re often more effective when paired with behavioural nudges that reshape ‘default choices’ and support sustainable habits.
The Green Nudge:
In a natural field experiment conducted by Antinyan and Corazzini across nine branches of a major Armenian grocery chain, 5,809 loyalty card holders were randomly assigned across several groups:
Control group – No intervention.
Environmental nudge – A letter explaining the harms of plastic, followed up by SMS reminders.
Financial bonus – A competition discouraging plastic bag use, organised among groups of 10 individuals. Group winners received 40 USD each.
Environmental nudge & bag – Same as the Environmental nudge group, plus a free reusable bag.
Financial bonus & bag – Same as the Financial bonus group, plus a free reusable bag.
The results: The researchers analysed checkout scanner data to track actual purchasing behaviour—offering a reliable, real-world measure of single-use plastic bag consumption.
The environmental nudge—a letter and SMS reminders—led to a ~12% reduction in plastic bag purchases compared to the control group.
The financial bonus was even more effective, cutting bag use by about 24%. However, it also reduced overall shopping activity: participants visited stores less often, bought fewer items, and spent roughly $20 less over six months.
When reusable bags were distributed, their use varied: participants in the nudge & bag group used theirs about 4.8 times on average. Usage was significantly higher in the bonus & bag group.
Importantly, reusable bag use scaled with shopping frequency—the more often people shopped, the more likely they were to reuse the bags.
These findings suggest that behavioural nudges can meaningfully reduce plastic use without disrupting overall shopping patterns, while financial incentives drive stronger behavioural shifts—but may come with trade-offs.
Do you know of any other nudges that curb single-use plastic? Feel free to comment or get in touch: hello@green-nudges.com
From Armenak Antinyan, Head of Behavioural Economics at Thames Water, and Luca Corazzini, Full Professor of Economics at the University of Milan-Bicocca. The researchers co-led the featured natural field experiment in Armenia and co-authored the study published in Ecological Economics.
