Cytology Program Research Guide : Evidence Based Medicine

Image from the Duke University EBP guide

Evidence-based medicine (EBM), also known as evidence-based practice (EBP) is the integration of best research evidence with clinical expertise and patient values.

• by best research evidence we mean clinically relevant research, often from the basic sciences of medicine, but especially from patient centered clinical research into the accuracy and precision of diagnostic tests (including the clinical examination), the power of prognostic markers, and the efficacy and safety of therapeutic, rehabilitative, and preventive regimens. New evidence from clinical research both invalidates previously accepted diagnostic tests and treatments and replaces them with new ones that are more powerful, more accurate, more efficacious, and safer.
• by clinical expertise we mean the ability to use our clinical skills and past experience to rapidly identify each patient's unique health state and diagnosis, their individual risks and benefits of potential interventions, and their personal values and expectations.
• by patient values we mean the unique preferences, concerns and expectations each patient brings to a clinical encounter and which must be integrated into clinical decisions if they are to serve the patient.

Straus, S. E., Glasziou, P., Richardson, W. S., & Haynes, R. B. (2019). Evidence-based medicine: How to practice and teach EBM.

The definition of EBM states the importance of obtaining the "best available evidence." The evidence hierarchy is an attempt to rank the health information resource/study designs with the highest quality sitting atop and the lower levels descending below. This hierarchy is helpful to guide evidence acquisition (literature searching) as well as providing clearer communication when discussing the landscape of health literature.

When it comes to prioritizing the evidence in any specific situation, clinicians will need understand the nuances of the evidence (reviews, studies) obtained. It is not uncommon for lower levels of evidence on the hierarchy to trump evidence sitting above: a hot-off the-press large RCT over an older meta analysis containing small studies.  

Armed with our well-built clinical questions, clinicians proceed to identify and obtain an answer from the evidence found in the health literature. There are thousands of health information resources are currently available; therefore, an understanding of the essential value of each resource type is required to determine when each one can best be applied.  Essentially, there are three general levels of literature:

Primary
Primary literature is where researchers publish their findings first. In the health field this is primarily in the form of journal articles outlining methodology, data, results, and conclusions. The evidence based approach emphasizes a hierarchy of evidence based on study types. When searching for single studies on a topic, clinicians should utilize database tools (limits and filters) to obtain the highest level of evidence to answer a clinical question. Examples: Randomized Controlled Trials, Cohort Studies, Case-Control Studies, Case Reports, Qualitative Studies

Secondary
Secondary literature summarizes the primary studies by appraising the relevant individual studies to answer a particular clinical question. In most cases, clinicians should initiate a search for answers to clinical questions with the secondary literature. Examples: Systematic Reviews, Meta-Analyses, Evidence-Based Guidelines, Some Clinical Database entries

Tertiary
There are now several online health information sources that accumulate the research (evidence) on clinical topics from the primary and secondary literature. These are often provide a very efficient way for clinicians to get up to speed on unfamiliar topics and filling holes in their knowledge base; however, clinicians should keep an eye on currency; the tertiary literature, by design, is lags behind the primary literature. Examples: Most guidelines and society statements, Most Clinical Database entries, Clinical Textbooks, Narrative Reviews