What does "palliative care" represent in research using secondary data?

While much research has been done regarding "palliative care" using retrospective cohort studies of large datasets, the data sources may not be capturing specialty palliative care services. This article aims to clarify what source data are used in such studies, how specialty palliative care services are determined to have been provided or not, and mismatches between the nature of the data and the interpretation of researchers. Major US data sources that are examined include cancer registries such as the National Cancer Database; health systems' internal data; state and nation-level hospital admissions data; and claims data from Medicare and commercial payers. Problematic studies are common. Many used cancer registry data and mischaracterized palliative intent for a given cancer treatment as "palliative care services." Dozens relied on the diagnosis code for "encounter for palliative care" which lacks adequate validity for use in research. Researchers, peer-reviewers, and research consumers are cautioned about these potential pitfalls that lead to meaningless or misleading research papers. Suggestions are made regarding more rigorous methods and trustworthy data sources and additional research that can lead to consensus among researchers on these issues.