The evidence base for practice guidelines is derived from two sources: research studies and clinical consensus. Where gaps exist in the research data, evidence is derived from clinical consensus, obtained through broad review of multiple drafts of each guideline (see Section VI). Both research data and clinical consensus vary in their validity and reliability for different clinical situations; guidelines state explicitly the nature of the supporting evidence for specific recommendations so that readers can make their own judgments regarding the utility of the recommendations. The following coding system is used for this purpose:

  • [A] Randomized, double-blind clinical trial. A study of an intervention in which subjects are prospectively followed over time; there are treatment and control groups; subjects are randomly assigned to the two groups; and both the subjects and the investigators are "blind" to the assignments.

  • [A–] Randomized clinical trial. Same as above but not double blind.

  • [B] Clinical trial. A prospective study in which an intervention is made and the results of that intervention are tracked longitudinally. Does not meet standards for a randomized clinical trial.

  • [C] Cohort or longitudinal study. A study in which subjects are prospectively followed over time without any specific intervention.

  • [D] Control study. A study in which a group of patients and a group of control subjects are identified in the present and information about them is pursued retrospectively or backward in time.

  • [E] Review with secondary data analysis. A structured analytic review of existing data, e.g., a meta-analysis or a decision analysis.

  • [F] Review. A qualitative review and discussion of previously published literature without a quantitative synthesis of the data.

  • [G] Other. Opinion-like essays, case reports, and other reports not categorized above.

The literature review process is explicitly described in every guideline, including statements concerning

  1. Basic search strategy (e.g., keywords, time period covered, research methodologies considered)

  2. Sources used for identifying studies (e.g., review articles, texts, abstracting and indexing services, Index Medicus, Science Citation Index, computer search services)

  3. Criteria for selecting publications (e.g., how many relevant publications were identified, whether all were reviewed, whether only prospective studies were selected)

  4. Review methods (e.g., whether publications were reviewed in their entirety or in abstract)

  5. Methods for cataloging reported outcomes (e.g., study design, sample characteristics, relevant findings)

The literature review will include other guidelines addressing the same topic, when available. The work group constructs evidence tables to illustrate the data regarding risks and benefits for each treatment and to evaluate the quality of the data. These tables facilitate group discussion of the evidence and agreement on treatment recommendations before guideline text is written. Evidence tables do not appear in the guideline; however, they are retained by APA to document the development process in case queries are received and to inform revisions of the guideline.


Citing articles are presented as examples only. In non-demo SCM6 implementation, integration with CrossRef’s "Cited By" API will populate this tab (http://www.crossref.org/citedby.html).
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