Study of the University of Bonn Shows a Clear Signal Builds More Trust and Increases Purchase Intention

To positively influence purchase decisions, sustainability labels must convey a clear signal rather than remain abstract. Using the EU’s “Green Leaf” organic logo as an example, researchers from the universities of Bonn, Newcastle (UK) and Corvinus (Hungary) demonstrate that simple design tweaks reduce consumers’ uncertainty, bolster their trust in the products, and thus increase their willingness to buy. The two-study-paper appears in the journal "Agribusiness" and is already available online.

Labels for sustainable foods—such as organic, fair-trade or animal-welfare certifications—are meant to assure consumers that products meet specific social and environmental standards. “Many labels fail to do so because they either don’t attract attention, aren’t clear enough, or even cause confusion,” says Prof. Dr. Monika Hartmann, head of the Department of Agricultural and Food Market Research at the University of Bonn.

One case in point is the EU’s organic logo, known as the “Green Leaf.”
Introduced in 2010 to create a unified European market for certified organic products, it is mandatory unlike national organic labels. Yet a 2024 survey found that only 56 percent of EU citizens recognize the EU organic label—and just 45 percent know it signifies compliance with EU organic standards.

Study in seven countries: Do design changes clarify the message?

Together researchers from the Universities of Bonn, Newcastle and Corvinus tested whether minor design changes could strengthen the label’s message and effect. They added “BIO” or “ECO” (depending on language) inside the green, star-bordered leaf, and in a second variant also appended “EU-certified.”
Three groups—with a total of 9,500 respondents across seven EU countries—saw either the original logo or one of the modified versions. Participants rated each logo for clarity, trustworthiness, and usefulness in making an informed choice.

The result: in every country, both modified labels were judged clearer, more understandable, more trustworthy, and more helpful than the original logo.
“Interestingly, adding ‘EU-certified’ had no extra effect,” says Hartmann.
“Apparently, the original logo mainly lacks the unmistakable signal that it denotes organic.”

Study in Germany: What drives these perceptions?

In a second study of about 500 German participants, the researchers investigated the mechanisms behind the enhanced appeal of the modified labels. They asked additional questions about clarity, uncertainty, trust, and behavioral intentions. “We showed that signal clarity rose dramatically,” explains Hartmann, who is also a member of the University of Bonn’s Transdisciplinary Research Area (TRA) “Sustainable Futures.” “Almost
90 percent of respondents clearly identified the logo augmented with ‘BIO’
or ‘ECO’ as an organic mark—versus under 70 percent for the original EU logo.” The new label also significantly reduced uncertainty and increased trust. There was no direct significant effect of label modification on purchase intention; however, the results reveal a significant indirect effect, mediated by reduced uncertainty and increased trust.

A low-effort, high-impact intervention

From these findings, the researchers conclude that labels for sustainably produced goods must be clearly recognizable to aid consumer decision-making.
If they are not, modifying a label to enhance its clarity offers a comparatively simple and cost-effective way to encourage sustainable purchasing.

Participating Institutions and Funding

The study involved the University of Bonn, Newcastle University in England, and Corvinus University of Budapest, Hungary. It was funded by the European Union’s Horizon 2020 programme.

Publication: Monika Hartmann, Ching-Hua Yeh, Matthew Gorton, Barbara Tocco, Áron Török: “Enhancing Sustainability Label Effectiveness Through Logo Design Modification: An Analysis of the EU Green Leaf Logo”. Agribusiness, 2025, https://doi.org/10.1002/agr.70013