How do family and friends influence our sustainable consumption decisions? Using an innovative and multidisciplinary methodological approach, the Doctoral research of Pedro Ribeiro shows that our close social circle plays a decisive role (often unconsciously) in shaping consumption behaviours. By combining Applied Psychology, Engineering and Neuroscience, the research opens up new perspectives for the design of public policies and more effective social marketing strategies to promote sustainable development.
Pedro Ribeiro recently completed the International PhD in Applied Psychology at the Faculty of Education and Psychology of the Universidade Católica Portuguesa (FEP-UCP) with the thesis “Methodological Innovations in Multidisciplinary Consumer Research towards Sustainable Development: An Applied Psychology Perspective”.
This work, supervised by Patrícia Oliveira-Silva, a lecturer at FEP-UCP, proposes new approaches to the study of consumer behaviour in a context of transition towards sustainable development.
With an initial background in Engineering, the researcher Pedro Ribeiro developed an academic path strongly marked by interdisciplinarity, international collaboration and close links with industry, innovatively exploring the complexity of consumer decision-making processes.
From Engineering to consumer behaviour: the motivation behind the choice of topic
The motivation to research consumer behaviour arises from the articulation between the researcher’s academic background, which began in Engineering, and his desire to engage with new scientific contexts. Pedro Ribeiro explains that “coming from Engineering, contact with consumers and with industry was not particularly unfamiliar to me, but I studied it very much from the perspective of product design and consumer needs”.
His interest in consumer behaviour deepened through collaboration with the Human Neurobehavioral Laboratory (HNL), when he became familiar with the Recovery and Resilience Plan (PRR) projects in which the laboratory was involved, linked to the green transition of the Portuguese footwear and textile industries. It was in this context that the researcher became curious about the topic and began to take an interest in how consumers make decisions in environments with countless stimuli, recognising that “there are countless stimuli to which the consumer is exposed that complicate their decision-making and make their main influences unpredictable”.
Methodological innovation to study a complex phenomenon
One of the central contributions of Pedro Ribeiro’s doctoral thesis lies in the innovation of the methodologies applied to the study of consumer behaviour.
This path initially involved a process of scientific redefinition. “At the beginning of the PhD I had an identity crisis: “What am I, an engineer, doing in a PhD in Psychology?”, he recounts. The answer to this question emerged through dialogue with his supervisors, as well as through analysis of the existing literature on consumer behaviour.
According to Pedro Ribeiro, the study of consumers remains excessively dependent on isolated self-report methodologies, which “limits theory to consumers’ perceptions”. To overcome this limitation, the PhD integrated methods from various fields, including biomedicine, psychology and sociology, allowing long-standing problems to be analysed through a new lens.
An international and truly interdisciplinary doctorate
The international dimension of the PhD was crucial to the scientific richness of the work developed. For the researcher, the main value of this international component was the possibility of assembling a supervisory team with very distinct competences, something that would have been more complex within a PhD conducted in a single country or institution.
“I believe that having a neuroscientist, a statistician and an anthropologist on my team gave my work a very special quality,” he emphasises.
This diversity within the team made it possible to identify and avoid biases arising from different disciplinary areas, as well as to promote ongoing discussion with supervisors regarding the methods to be used and analytical approaches to be developed.
Thus, the plurality of perspectives from different fields proved particularly relevant in an area such as consumer behaviour, which naturally brings together contributions from economics, marketing, psychology, sociology and neuroscience.
Implications of the research for public policies and social marketing strategies
Among the main findings of the work, Pedro Ribeiro highlights the notion of the importance of the close social circle, namely family and friends, in decision-making related to consumption behaviours. Even subconsciously, these agents play a central role in our individual decision-making.
In the current context marked by social polarisation, the researcher argues that strategies to promote sustainable development must go beyond the logic of individual choice. “Policies should focus on communities and social norms, and not only on individual consumer choice,” he argues, stressing the relevance of social marketing approaches such as “bring your friend” initiatives, more oriented towards the individual’s immediate social group.
Pedro Ribeiro also identifies a central challenge for Applied Psychology in aligning human behaviour with planetary boundaries: the need to establish bidirectional communication channels between consumers and companies.
At a time of cost-of-living crisis, Pedro Ribeiro argues that Applied Psychology can take on a fundamental mediating role in the transition towards more sustainable models of consumption and production.
The doctoral thesis was defended on 26 January 2026 at the Universidade Católica Portuguesa.