Evidence-Based Medicine: Searching for Evidence

Clinical information is often divided into two types of information: background information and foreground information. Background questions are needed when searching for general information on symptoms, disease progression, pathophysiology, or epidemiology. These questions generally require answering who, what, where, why and how. Background information is well accepted and consistent.

Example: What are the symptoms of gastroparesis?

Foreground questions are needed when answering question regarding clinical care of a specific patient. Answering foreground questions require specific knowledge and often change with the addition of new research. With foreground questions, it helps to develop a focused question using PICO.

Example: In adult patients with Allergic Rhinitis, are Intranasal steroids more effective than oral antihistamines in the management of symptoms?

Literature's Nuances

Thousands of articles are published everyday, which means there is an every growing amount of information you as a health care professional will have to navigate and appraise. All research is based on around primary, secondary, and tertiary information sources. The distinction between these source types depends on the originality of the information being communicated and the proximity to the original source of information. As you progress through your clinical career, you will use all of these resources types. You will learn what questions are best answered by primary, secondary, and tertiary sources.

• Primary literature reports original research. Basic science and biomedical primary sources are documents or records that synthesize a study, experiment, trial, or other research project. These sources are often written by the researcher(s) who conducted the study or ran the experiment, and are often testing a hypothesis. This type of information is not pre-appraised, therefore you will be required to appraise the information for validity. One article describing causation is not always enough to effect decision making. If you are looking at individual articles consider appraising the Methods, Results, and Discussion. When reviewing primary literature, you should be able to find a description of the patients included and excluded, total number of patients studied, basic data so calculations can be completed, limitations, and interpretation of results.
• Secondary literature analyzes, synopsizes, and synthesizes primary literature. The advantage of secondary literature is that the information has already been appraised by other professionals, though you always must appraise the methods used for appraisal. Basic science and biomedical primary sources are documents or records that synthesize a study, experiment, trial, or other research project. These sources are often written by the researcher(s) who conducted the study, ran the experiment, and are often testing a hypothesis. Methodologies and results should be comprehensive and descriptive.
• Tertiary resources synthesizes and compilations and will include the decisions made through primary and secondary research. This resources include textbooks, reference books, fact books, encyclopedias, and almanacs. 

Melnyk's Levels of Evidence

Level 1 - Evidence from a systematic review or meta-analysis of all relevant randomized controlled trials (RCTs), or evidence-based clinical practice guidelines based on systematic reviews of RCTs

Level 2 - Evidence obtained from at least one well-designed RCT

Level 3 - Evidence obtained from well-designed controlled trials without randomization

Level 4 - Evidence from well-designed case-control and cohort studies

Level 5 - Evidence from systematic reviews of descriptive and qualitative studies

Level 6 - Evidence from a single descriptive or qualitative study

Level 7 - Evidence from the opinion of authorities and/or reports of expert committees

From: Melnyk, Bernadette Mazurek, and Ellen Fineout-Overholt. Evidence-Based Practice in Nursing & Healthcare: A Guide to Best Practice.

Johns Hopkins Nursing Quality of Evidence Appraisal

Level I
Experimental study, randomized controlled trial (RCT) Systematic review of RCTs, with or without meta-analysis

Level II
Quasi-experimental Study
Systematic review of a combination of RCTs and quasi-experimental, or quasi-experimental studies only, with or without meta-analysis.

Level III
Non-experimental study
Systematic review of a combination of RCTs, quasi-experimental and non-experimental, or non-experimental studies only, with or without meta-analysis.
Qualitative study or systematic review, with or without meta-analysis

Level IV
Opinion of respected authorities and/or nationally recognized expert committees/consensus panels based on scientific evidence.
Includes:
- Clinical practice guidelines
- Consensus panels

Level V
Based on experiential and non-research evidence.
Includes:
- Literature reviews
- Quality improvement, program or financial evaluation
- Case reports
- Opinion of nationally recognized expert(s) based on experiential evidence

From:  Poe. S & White, K. (2010). "Table 1.1 JHNEBP Evidence Strength Rating Scale" in Johns Hopkins nursing evidence-based practice : implementation and translation (pp. 13). Indianapolis, IN : Sigma Theta Tau International.

Other Levels of Evidence Hierarchies

Essential Evidence Plus: Levels of Evidence
Oxford Centre for EBM: Levels of Evidence

Organizing your question before you start searching for an answer will save you searching time and effort. There are a structured formats for asking questions. Using this simple system will help you to create a "well-built" question. 

PICO

The most commonly used method in the evidence-based medicine process is PICO. PICO is a model that helps define a clinical question. The PICO Model is usually most useful for treatment questions. The table below breaks down the clinical question: In adult patients with Allergic Rhinitis, are Intranasal steroids more effective than oral antihistamines in the management of symptoms?

Concept Table

A Concept Table can help flesh out your EBM/EBP question, and ultimately improve your search strategy. The document below will help you transform your PICO question into a search strategy that can be used in PubMed.

Appraisal Resources

So you have found an article in PubMed that describes a treatment that could be beneficial to your case? Since it is a single study, and therefore not pre-appraised information, you will have to appraise the validity of the literature yourself. You will need to analyze the methods, results, discussion sections of the article. To learn more about breaking down the appraisal process check out this resource: Breaking Down Appraisal: Considerations for Appraising Primary Literature