National Cancer Institute


Information about how to weigh the strength of the evidence obtained in supportive and palliative care studies.

This PDQ cancer information summary for health professionals provides comprehensive, peer-reviewed, evidence-based information about the formal ranking system used by the PDQ Editorial Boards to assess evidence supporting the use of specific interventions or approaches. It is intended as a resource to inform and assist clinicians who care for cancer patients. It does not provide formal guidelines or recommendations for making health care decisions.

This summary is reviewed regularly and updated as necessary by the PDQ Supportive and Palliative Care Editorial Board, which is editorially independent of the National Cancer Institute (NCI). The summary reflects an independent review of the literature and does not represent a policy statement of NCI or the National Institutes of Health (NIH).

Levels of Evidence: Supportive & Palliative Care

Levels of Evidence: Supportive and Palliative Care Studies

Introduction

The PDQ supportive and palliative care information summaries provide descriptions of the pathophysiology and treatment of common physical and psychosocial complications of cancer and its treatment, including complications such as pain, anxiety, depression, fatigue, and nausea and vomiting. Each PDQ health professional summary generally includes an overview; information about etiology, assessment, and management; and citations to published literature.

The supportive and palliative care of cancer patients and their families and caregivers can involve the identification and mitigation of physiological, psychological, and spiritual needs.

References cited in the PDQ supportive and palliative care information summaries are drawn primarily from the peer-reviewed biomedical literature. The quality and reliability of such published reports can vary considerably. To help readers assess the strength of findings from clinical research studies, levels-of-evidence rankings are often employed. These rankings generally take into account the strength of a study’s design and the strength of the clinical outcome(s) measured. Clinical research in supportive and palliative care is feasible in some settings but difficult to conduct in others, such as at the end of life. Furthermore, as in other areas of medicine, supportive and palliative care decisions must be made in the context of existing evidence, which may be weaker than ideal.

In general, the quality of evidence depends on:

  • The appropriateness of the study to the question being asked.
  • How well the study was designed, implemented, analyzed, and interpreted.

For evaluating outcomes of both medical and psychosocial interventions, the strongest evidence is obtained from well-designed, well-conducted randomized clinical trials. For evaluating other questions, particularly those related to symptom management, well-designed descriptive studies may provide the strongest evidence practicable. Particular elements of study design, such as the nature of the population being studied or the duration of observation, may be crucial to assessing the quality of a study. Reviews of studies will indicate the level of evidence and any confounding design issues.

During the early phases of research in a new area, information relevant to the needs of patients and clinicians may come from a limited number of reports and data of varying strength. This information may include evidence from:

  • Well-designed prospective studies (e.g., randomized trials, nonrandomized trials, cohort studies, and case series).
  • Cross-sectional studies (e.g., correlational designs using various levels of analytic sophistication).
  • Retrospective studies (e.g., case-control studies, case series, and case reports).

The studies may be interventional, may be observational, or may involve provider or patient self-reports or record reviews.

In some cases, the best available evidence may reflect clinical/professional experience or expert consensus opinion. All sources may yield information relevant to patients and clinicians, who may be required to make management decisions before the best possible evidence is available.

In view of this complexity, the PDQ Supportive and Palliative Care Editorial Board took a pragmatic approach to defining the levels of evidence that it would utilize. The levels used by the Board focus primarily on the strength of a study’s design as appropriate to the questions being investigated. These levels should be easily understood by health professionals and serve as a starting point for discussing the strength of study results.

Study Design Categories, Definitions, and Levels of Evidence

Changes to This Summary (06/17/2015)

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.

Editorial changes were made to this summary.

This summary is written and maintained by the PDQ Supportive and Palliative Care 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.

About This PDQ Summary

Purpose of This Summary

This PDQ cancer information summary for health professionals provides comprehensive, peer-reviewed, evidence-based information about the formal ranking system used by the PDQ Editorial Boards to assess evidence supporting the use of specific interventions or approaches. It is intended as a resource to inform and assist clinicians who care for cancer patients. It does not provide formal guidelines or recommendations for making health care decisions.

Reviewers and Updates

This summary is reviewed regularly and updated as necessary by the PDQ Supportive and Palliative Care Editorial Board, which is editorially independent of the National Cancer Institute (NCI). The summary reflects an independent review of the literature and does not represent a policy statement of NCI or the National Institutes of Health (NIH).

Board members review recently published articles each month to determine whether an article should:

  • be discussed at a meeting,
  • be cited with text, or
  • replace or update an existing article that is already cited.

Changes to the summaries are made through a consensus process in which Board members evaluate the strength of the evidence in the published articles and determine how the article should be included in the summary.

Any comments or questions about the summary content should be submitted to Cancer.gov through the NCI website's Email Us. Do not contact the individual Board Members with questions or comments about the summaries. Board members will not respond to individual inquiries.

Levels of Evidence

Some of the reference citations in this summary are accompanied by a level-of-evidence designation. These designations are intended to help readers assess the strength of the evidence supporting the use of specific interventions or approaches. The PDQ Supportive and Palliative Care Editorial Board uses a formal evidence ranking system in developing its level-of-evidence designations.

Permission to Use This Summary

PDQ is a registered trademark. Although the content of PDQ documents can be used freely as text, it cannot be identified as an NCI PDQ cancer information summary unless it is presented in its entirety and is regularly updated. However, an author would be permitted to write a sentence such as “NCI’s PDQ cancer information summary about breast cancer prevention states the risks succinctly: [include excerpt from the summary].”

The preferred citation for this PDQ summary is:

National Cancer Institute: PDQ® Levels of Evidence for Supportive and Palliative Care Studies. Bethesda, MD: National Cancer Institute. Date last modified . Available at: http://www.cancer.gov/publications/pdq/levels-evidence/supportive-care. Accessed .

Images in this summary are used with permission of the author(s), artist, and/or publisher for use within the PDQ summaries only. Permission to use images outside the context of PDQ information must be obtained from the owner(s) and cannot be granted by the National Cancer Institute. Information about using the illustrations in this summary, along with many other cancer-related images, is available in Visuals Online, a collection of over 2,000 scientific images.

Disclaimer

The information in these summaries should not be used as a basis for insurance reimbursement determinations. More information on insurance coverage is available on Cancer.gov on the Managing Cancer Care page.

Contact Us

More information about contacting us or receiving help with the Cancer.gov website can be found on our Contact Us for Help page. Questions can also be submitted to Cancer.gov through the website’s Email Us.


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