Levels of Evidence for Adult and Pediatric Cancer Treatment Studies (PDQ®)–Health Professional Version

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Changes to This Summary (05/19/2017)

The PDQ cancer information summaries are reviewed regularly and updated as new information becomes available. This section describes the latest changes made to this summary as of the date above.

Strength of Study Design

Revised text in the third type of study design to include case series or other observational study designs.

Revised text to include nonconsecutive cases or other observational study designs (e.g., cohort or case-control studies).

Revised text to state that the clinical experiences always raise issues of patient selection and comparability with other populations. In order of generalizability to other populations are population-based studies that have a definable population, nonpopulation-based but consecutive series, and nonconsecutive cases. Added that some study designs (e.g., cohort and case-control studies) have internal-control study subjects, and the strength of conclusions that can be drawn from these studies depends on the homogeneity of patients managed with the interventions. If the subjects are sufficiently comparable, stronger conclusions are possible than with case-only series with no internal comparison group or with case-only series that are compared to historical controls.

This summary is written and maintained by the PDQ Adult Treatment Editorial Board, which is editorially independent of NCI. The summary reflects an independent review of the literature and does not represent a policy statement of NCI or NIH. More information about summary policies and the role of the PDQ Editorial Boards in maintaining the PDQ summaries can be found on the About This PDQ Summary and PDQ® - NCI's Comprehensive Cancer Database pages.

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