In this report, we document three examples from our own experiences of PPI in health economics, discuss the practical approaches, reflect on what we learned and, finally, make suggestions for researchers seeking PPI in economic studies. We focus on three case studies of projects that were funded by the National Institute of Health Research (NIHR): a feasibility study of a parenting programme to prevent home injuries in pre-school children , a feasibility randomized controlled trial (RCT) of a complex intervention to improve the management of children presenting to primary care with acute cough  and Parent-to-Parent support, a study of the benefits and costs of a one-to-one peer-support service for parents of disabled children [15,16,17] (Table 1). As with any study where public involvement is planned, researchers undertaking health economic research need to consider who to involve and why, when and how to involve them (see Box 1) . We describe this process in the context of our own experiences of PPI and working with young people and their families, in each case reporting in accordance with the Guidance for Reporting Involvement of Patients and the Public 2-short form (GRIPP2 SF) checklist  (Table 2).
Case Study 1: The FAST (First-aid Advice and Safety Training [FAST] Parenting Programme) Study
Why? The primary outcome for the study was parent-reported child injuries sustained at home. As parents may have been concerned that frequent reporting of injuries would lead to judgements about their parenting ability, PPI was crucial to understand how to engage parents in disclosing injuries and recording which healthcare services had been used. The economic component of the feasibility study determined the resource utilisation and costing data that would need to be collected in a full trial.
Who? A parent advisory group (PAG) was formed of young parents with one or more children under the age of 5 years. Facilitated through, and based at, a children’s centre, the PAG involved parents who may not otherwise have engaged in research.
How? To capture both the primary outcome (parent-reported injuries occurring at baseline and during follow-up) and measures of benefit and resource use, PAG members directly influenced the development of a proposed injury diary and its transformation into a calendar that could be attached to a fridge door or a wall. The calendar design (appearance, content, utility) evolved incrementally over the sessions to reflect parent needs and feedback from PAG members. The final design enabled parent participants in the study to code multiple child injuries, noting when and where they occurred and what the carer did in response, including healthcare service use in a concise format that was usable over several months of follow-up.
Outcome of PPI: The involvement of the PAG resulted in a data-collection tool that was acceptable to parents and well completed (151 injuries reported from 22 households), indicating that parental self-recording can be used to capture the health and family resource use required for economic evaluation. The PPI involvement illustrated the burden of injuries to families and changed the economic perspective of the proposed future trial from a health perspective to a societal one to capture the broader non-national health service (NHS) costs and benefits associated with injury prevention. The potential to use the calendar in future evaluations of injury-prevention initiatives was recognised.
Critical reflection: In this study, parents voiced concerns that ultimately led to the removal of a resource use question item. However, it may not always be appropriate to entirely remove an item (or otherwise depart from a study plan) based on what patients and members of the public report they do not like. It is plausible that there may be more objection if the rationale for the economic study is poorly described and/or if the PAG does not understand the justification for the data collection. Researchers therefore need to allow time for explanation and problem solving.
Case Study 2: The CHICO (CHIldren’s COugh) Study
Why? The rationale for PPI input was to identify what resources are required to care for children with cough and to establish the best mode of delivery of both a resource use questionnaire and a health utility measure for this population.
Who? A PAG was formed after a researcher approach to an existing parent and toddler group held in a community venue.
How? The PAG met twice yearly throughout the study. Sessions were carried out by two members of the study team who liaised with the study health economist. Meetings incorporated a PAG role-play session, with observing PAG members encouraged to comment aloud as a list of proposed questions composed by the trial health economist were asked of one of the mothers. Parents’ responses revealed that certain questions on household income were intrusive and that technical labels for different types of healthcare were unfamiliar. Further consultation with parents shaped the format, content and mode of delivery of parent/carer and child materials.
Outcome of PPI: The involvement of the PAG suggested that an online resource use form would work better with parents and that an appealing booklet version of the health utility measure (the CHU-9D [Child Health Utility-9 Dimensions]) [21,22,23] would be easier for 7- to 11-year-olds. Parents were uncomfortable reporting details of earnings, and these sensitivities led to questions about personal income being omitted from a final version of the resource use survey (information on personal finances is not strictly necessary to capture the opportunity cost of time off work, as an imputed wage rate is commonly used). Plain English alternatives were found for technical labels. The PAG provided feedback regarding font, graphics and images that was taken to a graphic designer to make completing the survey more engaging.
Critical reflection: Researchers identified mothers easily by asking an established mother and toddler group who was willing to be involved. Such a selection method may be more suited to common illnesses and more minor ailments. However, there may be an issue with the representativeness of samples based in single community settings.
Case Study 3: The Parent-to-Parent Support Study
Why? The idea to carry out research about peer support for parents of disabled children grew from a topic raised by a parent. The aim of the economic component of the study was to investigate what time, resources and money is needed to provide a one-to-one peer-befriending service for parents of disabled children. The broader aim of the evaluation as a whole was to conduct the research in collaboration with Face 2 Face, a service provided by the charity Scope to connect parents with disabled children to emotional and practical support.
Who? A study stakeholder group was formed by the Face 2 Face coordinator inviting all parents with disabled children who were active befrienders in Exeter and mid and east Devon. This helped ensure data collection was relevant and likely to be feasible.
How? Work sampling is a measurement technique that allows the proportion of time spent by people on particular activities to be estimated and can “provide important insights into the cost analysis of complex interventions” . Work sampling was used in the study to (1) estimate, in a systematic manner, the amount of time that befrienders spent in befriending activities and; (2) give a detailed picture of how befrienders spent their time and how they divided their time between different activities in providing the service. Prior to the work sampling, two involvement meetings were held with befrienders, the lead researcher and the health economist to identify the main befriending activities (e.g. visits to parents, making phone calls on behalf of parents, paperwork, travelling). All befrienders involved in providing the parent-to-parent service were invited to these meetings. Based on the outcomes of these meetings, a work sampling form was created for completion by the befrienders in the study regarding the amount of time they spent on each of these main activities.
Outcome of PPI: The involvement of the befrienders with disabled children during the course of the study played a significant role in influencing which data were included in the costing analysis, steered how the data were collected and helped provide an economic explanatory framework. Involving people in deciding the categories for work sampling led to the identification of the main activities and the amount of time spent in these activities from the perspective of parent befrienders themselves. The data collected showed the high proportion of time that befrienders spent supporting each other (‘mutual support’) and being supervised by the befriender co-ordinator. This was clearly a resource requirement in providing the service, which was accounted for in the intervention costing, and which was unlikely to have been identified if the method of costing had been more led by researcher-based assumptions. This unanticipated perspective afforded by PPI facilitated understanding and appreciation of the resources needed to provide the service and why they were needed.
Critical reflection: The befrienders were surprised to be asked to be involved in the costing aspect of the research, stating it was something they were not used to being involved with. In the first group meeting, jargon was initially a barrier, and the project lead ended up spending time ‘translating’ the health economics terminology. However, by the second meeting, these issues were ironed out and the health economist had a clearer way of providing explanations. What was notable was the enthusiasm of the befrienders to help steer this part of the project.