Exploring generalizability in a study of costs for community-based palliative care

Context: Palliative care researchers face challenges recruiting and retaining study subjects. Objectives: This article investigates selection, study site, and participation biases to assess generalizability of a cost analysis of palliative care program (PCP) clients receiving care at home. Methods: Study subjects' sociodemographic, geographic, survival, disease, and treatment characteristics were compared for the same year and region with those of three populations. Comparison I was with nonstudy subjects enrolled in the PCP to assess selection bias. Comparison II was with adults who died of cancer to assess study site bias. Comparison III was with study-eligible persons who declined to participate in order to assess participation bias. Results: Comparison I: When compared with the other 1010 PCP clients, the 50 study subjects were on average 3.6 years younger (P = 0.03), enrolled 70 days longer in the PCP (P < 0.001), lived 6.7 km closer to the PCP (P < 0.0001), and were more likely to have cancer (96.0% vs. 86.4%, P = 0.05). Comparison II: Compared with all cancer decedents, the 45 study subjects who died of cancer were on average 7.0 years younger (P < 0.001), lived 2.7 km closer to the PCP (P < 0.001), and were more likely to have had radiotherapy (62.2% vs. 33.8%, P < 0.0001) and medical oncology (28.9% vs. 14.8%, P = 0.01) consultations. Comparison III: The 50 study subjects lived on average 42 days longer after their diagnosis (P = 0.03) and 2.6 km closer to the PCP (P = 0.01) than the 110 eligible persons who declined to participate. Conclusion: If the study findings are applied to populations that differ from the study subjects, inaccurate conclusions are possible.