About PDQ-Evidence

What is PDQ-Evidence?

PDQ (“pretty darn quick”)-Evidence facilitates rapid access to the best available evidence for decisions about health systems. It includes systematic reviews, broad syntheses of reviews (including evidence-based policy briefs), primary studies included in systematic reviews and structured summaries of that evidence.

PDQ-Evidence was developed and is maintained by systematically searching PubMed and other databases for relevant systematic reviews and broad syntheses of reviews. The search strategies that are used and the methods that are used to screen the search results and select records for inclusion are described here:

The aim of PDQ-Evidence is to provide rapid access to systematic reviews of health systems evidence. A unique feature of PDQ-Evidence is that it links together systematic reviews, broad syntheses of reviews and primary studies, thus providing a highly efficient method for searching. In addition, it includes translations of the titles and abstracts of included records to facilitate searching in different languages and it is continually updated by searching multiple sources of systematic reviews and broad syntheses of reviews.

PDQ-Evidence is not a comprehensive database of health systems research. It only includes primary studies that have been included in a systematic review.

How to use PDQ-Evidence

Searching

PDQ-Evidence can easily be searched by typing terms into the search box and clicking on the “Search PDQ-Evidence” button. If more than one word is included in the search query, the results will only show articles that include all of the words that are used in either the title or the abstract.

If few or no articles are found, the search can be broadened by clicking on the link under the search box: “Click here to broaden the search”. Doing this will show articles that include any of the words that are used in either the title or the abstract prioritized according to several factors, such as proximity between words, frequency of each word, etc. The search can also be broadened by using fewer terms in the query, by adding synonyms (and then clicking on “Click here to broaden the search”) or by using Advanced search and OR between terms.

If many irrelevant articles are found, the search can be narrowed by putting the terms in quotes (e.g. “community health workers”). This will show articles that include exactly the phrase that is in quotes.

By clicking on “Advanced search” it is possible to restrict the search to specific fields (title, abstract, title and abstract, or author, etc) and to use Boolean logic; i.e. choosing whether to search only for articles that include more than one term (using AND) or to search for articles that include any of two or more terms (using OR).

Unique feature: article connections

Additional articles can also be found by opening the abstract for relevant articles that are found and then clicking on one of the boxes on the right showing evidence related to the article. This will show the following connections

Broad syntheses are linked to:
Systematic reviews are linked to:
Primary studies are linked to:

Terms and Conditions

PDQ-Evidence does not provide specific healthcare advice or recommendations, but rather information to inform health system decisions. We do not assume any legal liability or responsibility related to the use of this information.

We do not guarantee or assume any legal liability or responsibility for the accuracy, completeness or usefulness of any information that is found searching PDQ-Evidence.

We do not endorse or recommend any commercial products or services. The views and opinions of individual authors do not necessarily reflect those of PDQ-Evidence or the people behind PDQ-Evidence. The PDQ-Evidence name and logo may not be used for advertising or product endorsement purposes.

Who are we?

The following people have contributed to the development of PDQ-Evidence:

Most of the technical developments rely on the software and collaborators of the Epistemonikos project. The search and identification of studies was partially funded by the European Commission’s 7th Framework Programme (Grant agreement no 222881) through the SURE project (Supporting the Use of Research Evidence for Policy in African Health Systems).. Additional support has come from the Norwegian Agency for Development Cooperation (Norad) and the Norwegian satellite of the Cochrane Effective Practice and Organisation of Care (EPOC) group.

What is included in PDQ-Evidence?

We include systematic reviews and broad syntheses of systematic reviews that that address an explicit question about health systems or population health, including:

We include systematic reviews and broad syntheses of systematic reviews of questions about health system problems, the effects of health system or population health interventions, barriers to and facilitators of those interventions, and the effects of implementation strategies.

We exclude systematic reviews and broad syntheses of systematic reviews that address clinical questions, including questions about the effects of clinical interventions, diagnostic tests, prognosis and aetiology.

Systematic Reviews

Systematic reviews are summaries of research evidence that address a clearly formulated question using systematic and explicit methods to:

Systematic reviews of research evidence constitute a more appropriate source of research evidence for decision-making than the latest or most heavily publicized research study. Advantages of systematic reviews include:

Broad syntheses of reviews

Broad syntheses of reviews are summaries of systematic reviews that address broad questions using systematic methods to:

Evidence-based policy briefs

Evidence-based policy briefs bring together ‘global’ research evidence (from systematic reviews) and local evidence to inform deliberations about health policies and programmes

They begin with a policy problem and summarise the best available evidence to:

Advantages of evidence-based policy briefs include:

Primary Studies

Primary studies in PDQ-Evidence include all of the studies that met the inclusion criteria for the systematic reviews in PDQ-Evidence.

The only limitations for inclusion of primary studies in PDQ-Evidence are those that were established by the review authors. We have not excluded studies based on publication status, language of publication, year of publication or study design beyond whatever exclusion criteria were used by the review authors.

Structured Summaries

Structured summaries of broad syntheses, systematic reviews and primary studies are prepared using standard headings and include critical appraisal and interpretation of the evidence that is summarised.

Typically these are prepared by someone other than the authors of the reports that are summarised and they contain more information than what is normally found in the abstracts written by the authors, which are also included in PDQ-Evidence.

The structured summaries that are included were not prepared specifically for PDQ-Evidence and are only available when they have been prepared by the authors of a report (e.g. executive summaries of evidence-based policy briefs) or by others (e.g. SUPPORT Summaries of systematic reviews for policymakers or DARE abstracts of systematic reviews).

Criteria for considering studies for this database

Types of studies

We consider the following types of studies for inclusion:

We include systematic reviews and broad syntheses of systematic reviews that address an explicit question about health systems or population health.

We exclude systematic reviews and broad syntheses of systematic reviews that address clinical questions, including questions about the effects of clinical interventions, diagnostic tests, prognosis and etiology.

Criteria for Systematic Reviews

We consider systematic reviews for inclusion if they fulfill the criteria below or are classified as a systematic review in an broad synthesis or structured summary.

Systematic review criteria (DARE. Accessed 04/08/2011, 2011, at http://www.crd.york.ac.uk/cms2web/AboutDare.asp)

>or =4 criteria (1-3 are mandatory)

  1. Were inclusion/exclusion criteria reported?
  2. Was the search adequate?
  3. Were the included studies synthesized?
  4. Was the validity of the included studies assessed?
  5. Are there sufficient details about the individual studies presented?

Additionally, the review has to:

Other terms used by authors to describe a systematic review include: meta-analysis, rapid review, evidence-based review, broad synthesis and literature review. We classify any review that meets the above criteria as a systematic review, regardless of the term employed by the authors.

Criteria for Broad syntheses of systematic reviews

We consider broad syntheses for inclusion if they fulfill the first criterion and one of criteria 2 to 4:

  1. A search strategy is described.
  2. Only systematic reviews are included.
  3. It is stated (or it is implicit) that for a specific question adressed, the primary studies will not be looked for if there are systematic reviews.
  4. Systematic reviews are the main focus of the article, and primary studies used to supplement the results of the included reviews.
  5. Additionally, the broad synthesis must provide a list of included reviews and, if relevant, studies, and summarize included systematic reviews.

Other terms used by authors to describe broad syntheses of systematic reviews include umbrella review, review of reviews, meta-reviews. We also consider evidence-based policy briefs (also called evidence briefs for policy) and guidelines, recommendations and consensus statements that meet the above criteria.

Criteria for Primary Studies

We include all studies included in systematic reviews and broad syntheses that fulfill the following criteria:

  1. Address a health problem in individuals, populations or health systems.
  2. Original data are provided (instead of using data generated in other studies).

All Primary studies included in systematic reviews that fulfill our inclusion criteria are entered into the database, independent of language or publication status.

If a list of included studies is not clearly provided by a systematic review or broad synthesis, we extract it from tables, annexes or from the text. If it is not possible to extract a list of included studies from the article (or there are doubts about this list, we contact the authors).

PDQ-Evidence search strategies

We search the following databases (no language or publication status restrictions are applied):

  1. Cochrane database of systematic reviews (CDSR)
  2. Database of Abstracts of Reviews of Effectiveness (DARE)
  3. Health Technology Assessment Database
  4. PubMed
  5. LILACS
  6. SUPPORT Summaries
  7. EPPI-Centre Evidence Library
  8. 3ie Systematic Reviews and Policy Briefs
  9. WHO Database
  10. Campbell Library
  11. SURE policy briefs
  12. European Observatory on Health Systems and Policies
  13. DFID
  14. NICE public health guidelines and systematic reviews
  15. Guide to Community Preventive Services
  16. CADTH Rx for Change
  17. McMaster Plus KT+
  18. McMaster Health Forum Evidence Briefs

For the following databases, we consider all records as potentially eligible: CDSR, DARE, HTA database, SUPPORT Summaries, EPPI-Centre Evidence Library, 3ie Systematic Reviews and Policy Briefs, Campbell Library, Evidencias en Pediatría, SURE policy briefs, DFID, NICE public health guidelines and systematic reviews, Guide to Community Preventive Services, CADTH Rx for Change, McMaster Plus KT+ and McMaster Health Forum. Given the very large number of records in PubMed and LILACS, we use search strategies that emphasise specificity rather than sensitivity for these databases (Appendix 1)

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