Background Many palliative care interventions that aim to enhance patient or family wellbeing are complex. This is often because the intervention involves multiple elements and it is unclear which of these elements contribute to its success. For example, an intervention that aims to support family caregivers may involve both emotional support and education. Different interventions, while being the same over-arching type of supportive intervention, may differ in what is provided to the caregiver. This makes it difficult in a systematic review to provide conclusions for palliative care practice. Qualitative evidence has potential in intervention design.

Aims Using a case example on promoting adherence to therapy, we present novel approaches that may help enhance understanding of complex interventions.

Methods In a table we combined (1) qualitative evidence synthesis on patients' suggestion on adherence promotion, with, (2) the content of interventions from multiple trials that aim to promote adherence. This created new data relationships, where the intervention content did and where it did not correspond with the content of effective interventions. We summarised the relationships narratively, statistically and using set-theory. We did this to compare techniques.

Main results Across the techniques we found consistent evidence that certain patient suggestions, if taken up in the intervention, may enhance its success. Many of these related to positive activities, such as clear instructions or emphasising the value of treatment. Suggestions absence in effective interventions were those in relation to more challenging aspects to adherence.

Conclusions Our approach of summarising pooled evidence on patients' views and intervention content provided new evidence on how to develop interventions. Our findings are strengthened as similar results, were found using different analytical techniques. Our approach provides a potential opportunity to make greater use of qualitative evidence on patients' and families' perspectives in relation to palliative care. The method may help accelerate better supportive interventions.