OMACS-PIL has provided some evidence that the formatting of a PIL can influence the perception of a study by potential participants, although the differences in consent rates were not statistically significant. The research team had hypothesised that PIL A would be most appealing to read, as it looked the ‘most professional’, but it was exactly this aspect that the PPI group did not like. The consistency between the quantitative finding and the PPI feedback reinforces the benefit of PPI being an integral part of research.
The sample size achieved was just short of the 1590 target. This is because, due to the lower than expected rates of consent across all PILs, the timing and mode of consent were changed to seeking face-to-face consent at the time of admission for the cardiac operation. The decision to change to face-to-face consent coincided with the sample size for the SWAT almost being met, and the decision was made to halt OMACS-PIL at this point.
The modest increase in recruitment with PIL B is consistent with other research on the design of consent materials. However, much of this previous research has included other interventions alongside changes to the PIL. For instance, in a RCT within the Avon Longitudinal Study of Parents and Children Study, potential participants were randomised to receive one of eight combinations of three interventions: (1) a prior-notification postcard or no contact, (2) a standard or professionally designed consent pack, and (3) a phone or postal reminder . Of these interventions, the most effective was the reminder phone call with a 6.4% higher response rate (95% CI + 2.3 to + 10.6%; p = 0.002). The professionally designed consent pack had some impact, increasing response rates by 2.7% (95% CI − 0.06% to 5.5%; p = 0.06), but the prior notification postcard had no effect. Phone call reminders can have significant resource implications, hence our decision not to include this as an intervention.
The START programme run by the Medical Research Council (MRC) also looked at the format of paper PILs, but this was an enhanced PIL where the wording was refined after several rounds of user testing [12, 13]. This approach has resource implications and of the work published so far, there have been only marginal improvements in recruitment [12, 15]. The Healthlines studies showed modest increases in a positive response to an invitation to participate in a study using the enhanced PIL, which, like OMACS-PIL, were not statistically significant (19% versus 16%, difference of 2.9%, 95% CI − 1.1% to 6.9% in the Healthlines depression study, n = 1364, and 24.0% versus 21.9%, difference of 2.0%, 95% CI − 4.3% to 8.4% in the Healthlines cardiovascular disease study, n = 671) . In Early CDT Lung Cancer Scotland, the proportion of patients who positively responded to the invitation was 224 / 1136 (19.7%) in the intervention group (optimised PIL) and 205 / 1126 (18.2%) in the control group (difference of 1.5%, 95% CI − 1.7% to 4.7%) . In addition to these MRC Start studies, the REFORM study concluded that there was limited evidence of the benefit of using optimised information materials on recruitment and retention rates  and the recently updated Cochrane review of methods to enhance recruitment to RCTs concluded that: ‘Using a tailored, user-testing approach to develop participant information leaflets makes little or no difference to recruitment’ . There has been a Cochrane review of methods to increase response rates to postal questionnaires , but this focused on the design of the questionnaire or the method of postage (e.g. first-class post) and not on the PIL provided to participants.
Resource implications for developing electronic media and the limited existing evidence that these media can improve recruitment  were the reasons that a multi-media approach was not explored in OMACS-PIL.
One area for concern in OMACS is that the overall response rate was much lower than expected. The expected response rate was based on similar work involving postal consent of cardiac surgery patients (Long-Term Monitoring Study), which had been as high as 80% . There are a few differences between the studies: the timing of the approach for consent was at 3 months versus 12 months after cardiac surgery, and the packs sent to OMACS patients had more documents and offered more choices in how to participate. The Long-Term Monitoring Study was conducted purely by post, whereas OMACS allowed participants to register, consent and complete questionnaires online if they preferred. This extra complexity may have contributed to the lower consent rate. The options were offered to allow participants to complete the study in the way most convenient to them, but it may be that the extra thinking involved meant that they did not take part at all. Again, this shows that researchers should not assume they know what patients want.
A limitation of this study is that not all of the three PIL formats would be suitable for all studies. The amount of information that can be contained in the format of PIL A is constrained. This was not a problem for OMACS as the information required to be conveyed about OMACS was limited, since OMACS is an observational study and not an RCT, and therefore was easily incorporated into the different formats. The format of PIL A may not be suitable for interventional trials where more information about the intervention and risk and benefits need to be included. Even for OMACS, the volume of information included in the PIL has increased since the SWAT was conducted, due to the requirements of NHS Digital for hospital episode statistics, which is a feature of the main study. The extra information was easily incorporated into PILs B and C but would have been more challenging to incorporate into PIL A due to the way that the information was presented and formatted. To make PIL B easier to use in OMACS and other studies and to remove the need for specialist software, we have now recreated the format in Microsoft Word (Microsoft Corporation), and this format is now being used for the host study.
The PPI work included was informal and the PPI group was relatively small. However, their opinions were consistent with the quantitative finding of the SWAT. The PPI group were not involved in the design of the PILs. However, the content of the PIL is under review and their views will be considered for future versions. We did not inform the potential participants about the SWAT as we felt that it would influence how they viewed the PIL, so we were unable to elicit potential participant views about the PIL formats.
A strength of OMACS-PIL is that the formatting of the PIL is something that can be improved in any study. A positive improvement in recruitment rates does not require rounds of user acceptability testing, as required by other projects (e.g. MRC START), or extra resources, as required with telephone contact or a multimedia approach, and could be achieved with PPI input. This means that it can be implemented with minimal or no impact on the study budget. OMACS-PIL was randomised and the participants were unaware of the SWAT. However, based on the results of OMACS-PIL and the other similar studies, any improvement in consent rates are likely to be small.