This study shows that most European birth cohort studies undertake some activities to promote wider engagement in their ongoing work, but this is most often restricted to project websites. Very few actively and regularly consult with their members. A few others have facilities for participant feedback in response to data collection. This suggests that participant consultation is low among the priorities for this group as a whole, albeit that some are making concerted attempts to do so.
Strengths and limitations
This study is the first to our knowledge that attempts to describe practice across a wide range of studies with similar methods on how they attempt to engage, inform and consult with their research participants. However, it has two significant limitations. Firstly, this study is restricted to practice in European cohorts, and so the description here excludes good practice elsewhere in the world. Secondly, we should be cautious to generalise from findings reported here, both because of the focus on European studies and because of the small number of studies for whom we have full information. Studies unknown to us, or who didn’t reply to our requests for information may have been undertaking participatory work which we don’t know about. However, we believe it is reasonable to assume that working in this way would increase the likelihood of responding to our requests for information, so it is likely we have described common practice among these studies. Within this small sample, the studies that undertook some form of consultation did not appear to differ from those that did not on their breadth of focus, time of inception, current age of participants, or size of cohort although larger cohorts more often had a formal approach to consultation.
Comparisons to other studies
We know of no other study which has attempted to audit and describe practice in engaging young participants across a number of studies sharing a study design. One study surveyed methods for identifying, measuring and reducing attrition in 38 longitudinal studies with older adults (aged over 55 years) . A range of activities similar to the ones identified here are reported (20 studies responded): information giving, newsletters, meetings, telephone calls, giving feedback about the study and summarising personal results, study websites, and incentives (fridge magnets, pens, money and calendars). Like us, they also found that variations in methods for reporting non-participation meant that cross study comparison was not possible, and that no data were available which suggested which strategies had been more successful .
A recent systematic review of strategies to increase retention in cohort studies shows that provision of financial incentives is the only strategy which has been shown to increase retention . These authors note that other strategies are common, including reminders, allowing alternative modes of data collection, and a combination of several approaches but that the effects of these are seldom systematically recorded. They further comment on the possible impact of an expectation of being involved in a study for a long period of time . In this context motivation to continue to take part might be influenced by participants’ feeling that the study is interesting, important, and pertinent to them. Documentation of methods to consult and engage with study members and any changes in response rates could usefully be recorded and reported in future.
Differing practice in gaining child assent or consent in six birth cohort studies has recently been described . Several researchers have considered the views of child participants or their parents involved in longitudinal health studies about informed consent to participate. In 2 studies of the views of parents whose children were enrolled in a birth cohort study, Swartling and colleagues found that while many parents wanted their children to be informed they were somewhat cautious about allowing their children authority to make decisions and some did not feel children should provide consent [30, 31]. Another study showed that when asked questions that were contextualized and concrete, child participants in a UK birth cohort study could understand and comment on ethical issues regarding consent for data storage and use [32, 33]. Similarly, qualitative research with child participants in a Danish cohort was used to suggest ways in which tests and procedures could be made more pleasant and interesting for children .
Finally, we located 5 studies of the experiences of adult participants in longitudinal studies [35–38]. These studies suggest there is an appetite for more involvement in research decisions among some. In interviews with adult (aged 50 years) participants from the National Child Development Study (NCDS), a birth cohort, around a third wanted more feedback from the study about the findings, presented in a way that was useful to them. These studies identify a number of common levers and barriers to study retention. Reasons for staying in studies included the ‘prestige’ of being part of an important study , a commitment to the greater good by contributing to research , and a sense of belonging or loyalty to the study .
In contrast, questions and questioning that they viewed as intrusive , where the structure and purpose of survey items were unclear to respondents , disillusionment with past participation, or unpleasant past experiences with survey completion and a lack of commitment to the survey  caused study drop out. These findings confirm our belief that greater involvement in research planning is likely to increase study participation. Participants commented that the decision about what to observe in research is down to whether “the powers that be” look kindly upon this activity (P149, p. 13 ). They also comment on how poorly worded questions affected both data quality and created a barrier to participation:
In the last one there was a question about how often do you see your children, …I had to put like I only saw him three times a year or something, which it was wrong, because I see him for long times when I see him….he’s at university …. but the form wouldn’t allow that. And I feel quite upset about it really though P351] .
Implications for cohort research groups
This study suggests that while most birth cohorts put in place methods to keep participants informed about the research they are involved in through study websites and newsletters, very few are creating opportunities to hear from their participants. Where cohort members are still very young consultation with their parents could be undertaken, but seldom is. Methods currently used range from simply providing the opportunity to enter text responses after completing a round of data collection to informal and formal mechanisms for consulting with participants. The success of these methods in either increasing participant engagement and retention, data quality, or in influencing research conduct have not been assessed to our knowledge. While calls for greater engagement in the research process are often value based and therefore do not rely on demonstrating efficacy, data on the relative success of different methods would be valuable and research documenting impact would be important.
In the absence of evidence to support selection of particular methods, it may be useful for those cohorts with younger members or those who undertake less participation to learn from those cohorts which undertake more engagement in planning for the future. This would allow, for example, anticipating and preparing for the transition from parent consent for infants, to assent and consent from children themselves.
The barriers to increased participation raised by the cohort researchers in this study are not unique to this study design. Barriers to involving children and young people in research are well outlined (and countered) by Kellett in her account of the work of the Children’s Research Centre. She reports concerns about children’s’ skills and competency, time and resource constraints, and worries that their participation will be meaningful . Involving young people can require skills that are more commonly associated with a participation officer than a researcher. As well as practical constraints, the gap between the knowledge systems of research and participation are known to create barriers to meaningful collaboration [8, 39, 40]. However, these barriers have been addressed in non-cohort studies [7, 9, 20, 21, 41] and examples of innovative practice showcase the output of young people working as researchers .
Through EUCCONET , European researchers are beginning to share practice on participant retention in birth cohorts, but not yet on participant consultation. Practical guidance exists for increasing involvement [18, 19] and lists of resources are provided by UNICEF  and INVOLVE (a national advisory group that supports greater public involvement in UK health research) . Changes need to be meaningful, but do not need to be large; current efforts to retain study members using Facebook [46–48] and family events could be used to create opportunities for contributions from cohort members without challenging some of the concerns of researchers regarding ethics and Hawthorne effects. Development of methods in this field is timely and would facilitate cooperation with existing and new major projects.