Table 2.

PPI contributors’ perceived roles and mechanisms of impact

Perceived role	Proposed mechanism of impact	Illustrative quote(s)
The expert in lived experience	Through their lived experience of a condition, PPI contributors are able to consider the acceptability and feasibility of research proposals for the target population	‘And many of these researchers and scientists only ever see [motor neurone disease] down a microscope, put in a Petri dish. But its meaning and its effect is unknown to them. I, on the other hand, am an expert of what it is to live and to die with motor neurone disease. And that does have a value to research’. (P03, carer) ‘…there was a piece of research about eating in dementia…and they were thinking, is it better for a dementia person to eat at lunch time rather than in the evening? […] And I said… “I don't think this study's going to work, this food study… because a dementia person will not sit down at meal times, at lunchtime, and eat a full meal.” […] And they must have listened because like I said they did take it off, they didn't bother with it’. (P22, carer)
The creative outsider	PPI contributors bring a fresh perspective from outside the research system, and can help to solve problems by thinking ‘outside the box’	‘By taking non‐experts into any field you can possibly get a whole leap forward because somebody suggests you look outside the box and you look at it from a different perspective’. (P11, patient/carer) ‘Members of the public – because of their different understandings – can come out with the most bizarre suggestions. But also, the most incredible suggestions that actually are the most important’. (P32, patient)
The free challenger	PPI contributors are able to challenge researchers without fear of consequences	‘We can ask the elephant in the room question. We can say, “Well why not? Why can't you do this? Well why can't you do it that way?” We're not employed, we don't have to worry about the hierarchy in our jobs…We can challenge from a purely interested point of view, not worrying about the bosses or the NHS or anything really’. (P31, patient) ‘A lot of academics in that group would have a stake in going forward with the leader because their jobs… it depends on being seen in a good light by the leader. The great advantage of the citizen researcher is that we don't. We are volunteers, we can speak truth to authority without danger of retribution…’ (P24, public)
The bridger	PPI contributors bridge the communication gap between researchers and patients or the public, making research more relevant and accessible	‘That's one of the main contributions that lay people can make, “What does that mean? What does that mean for me? What does that mean for my friends? What will it mean for the future? Will it make me better? Will it make my auntie better?” […] And sometimes clinical researchers may not… have thought of the issues with that simplicity so I'm I suppose making a case for public and patient involvement to make research as simple as possible in how to understand it, what it's going to achieve and how you tell the public about it’. (P18, public)
The motivator	PPI contributors increase researchers’ motivation/enthusiasm, for example by emphasizing how the research will benefit people.	‘… I've seen researchers get really very excited about how real the whole thing seems as opposed to sort of theoretical and academic. So they can start to see how the research they're doing is really going to benefit people so it [PPI] gives a sort of extra sort of brilliance to it, it makes it more exciting and engaging’. (P12, patient)
The passive presence	PPI contributors can change the way that professionals think just by being present at meetings.	‘Sometimes, even if we're just there as a listener, not as an active contributor, but the professionals know that we are there, and they try to think from our perspective as well’. (P06, carer) ‘…Afterwards someone says, “You have no idea the difference that your being there, just being in a room, has made… People are stopping and listening to each other, not just you, in a different way.”’(P40, patient)