Who should I involve in my research and why? Patients, carers or the public?

Patient and public involvement in research helps to make it more relevant and useful to the end-users. Involvement influences the design, delivery and dissemination of research, ultimately leading to better services, treatments and care. Researchers are therefore keen to involve patients, carers and public in their work, but are sometimes uncertain about who to involve. Some confusion may arise from the terms used. The UK's catch-all term 'patient and public involvement' suggests this is a single activity, that perhaps both 'patient' and 'public' input are needed, or that either will do. The terms 'patient', 'carer' and 'public' have been defined, but are not used consistently. In fact there are many different contexts for involvement and many different kinds of decisions made, which then determine whose input will be most valuable.Clarity about the 'why' can help answer the 'who' question. However, not all researchers are clear about the purpose of involvement. While it is often understood to have a moral purpose, or to improve research quality, this doesn't always identify who needs to be involved. When learning is understood to be the purpose of involvement, then the most appropriate people to involve are those with relevant experiential knowledge. In research projects, these are people with lived experience of the topic being investigated. This could be patients, carers, members of the public or health professionals.In this article we discuss how involving people who do not have the relevant experiential 'lived' knowledge may contribute to ineffective or tokenistic involvement. These people are as likely as researchers to make assumptions, risking missing key insights or resulting in outcomes that are off-putting or even harmful to research participants.We conclude that greater attention needs to be given to the question of who to involve. Raising awareness of the significance of experiential knowledge and the contextual factors that determine whose input will be most useful will help everyone to understand their roles and improve the quality of involvement. It will help to maximise the opportunities for learning, increasing the likelihood of impact, and helping to achieve the ultimate goal of improved health and services.