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Levels of Evidence for Supportive and Palliative Care Studies (PDQ®)

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.

  1. Physiological complications currently addressed in the PDQ supportive and palliative care summaries include the following:
    • Cardiopulmonary syndromes.
    • Temperature fluctuation.
    • Gastrointestinal complications.
    • Metabolic disorders.
    • Lymphedema.
    • Nausea and vomiting.
    • Oral complications.
    • Pain.
    • Dermatological problems.
    • Sexual dysfunction.
    • Sleep abnormalities.
    • Malnutrition.
    • Dehydration.
    • Fatigue.
    • Cachexia.
    • Weight loss/weight gain.

  2. Psychological or behavioral complications currently addressed in the PDQ supportive and palliative care summaries include the following:
    • Anxiety.
    • Cognitive disorders.
    • Depression.
    • Grief issues.
    • Adjustment difficulties.
    • Post-traumatic stress disorder.
    • Tobacco dependence/smoking cessation.
    • Nutrition/weight management.
    • Substance abuse.

  3. Spiritual and religious concerns currently addressed in the PDQ supportive and palliative care summaries include the following:
    • Spiritual experience.
    • Religious beliefs.
    • Approaches to addressing these issues.

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.

  • Updated: August 26, 2010