The challenge of selection bias and confounding in palliative care research.

The early successes of hospital- and community-based hospice and palliative care programs have led to rapid growth of these services over the past several decades.1,2 This widespread adoption is generally seen as a positive addition to the care of patients with complex illness. However, the growth in palliative care and hospice programs creates challenges for research, especially in the use of randomized controlled trial (RCT) designs, which are deemed the gold standard of research methods because of their ability to control for biases in the estimates of treatment effects. As Carlson and Morrison3 noted in their introduction to this research methods series, sometimes RCTs can be impossible to conduct due to inherent challenges in recruiting seriously ill participants, or may not be ethically appropriate in the absence of clinical equipoise. To date, observational studies have provided much of the evidence demonstrating the effectiveness of palliative care interventions on outcomes including pain and symptom management,4–9 communication between clinicians, patients, and families,10–13 patient and family satisfaction with care,8,14 and on reducing the costs of care while maintaining or improving quality.8,15–20 Observational studies have been criticized for their methodological weaknesses, yet it would be a mistake to dismiss their use as they have and will continue to offer important insights into the real world of hospice and palliative care.