Evidence-Based Health Care: A Tutorial Part 1Presentation Transcript
Evidence-Based Health Care: A Tutorial
Joyce Condon , MLS, AHIP Reference Librarian
Exempla Saint Joseph Hospital Denver, Colorado USA Medical Library
Well-Built Questions The goal of this tutorial is to help you develop your searching skills to track down the best published evidence. This self-paced online course is designed for learners in all phases of their education.
Identifying the clinical issue
Defining a well-built question to address
the clinical issue
You must first ask good questions, then have a strategy to map them to the resources of evidence. Learn how to use PICO and clinical mapping to guide search strategy development and choice of databases to find the evidence.
You will learn:
how to identify a clinical issue,
define a well-built question to address the issue,
design a search strategy for the question
and select appropriate evidence resources
for the search.
The clinical question may require general background knowledge involving the who, what, when, where or why about a disease or disease process. Background questions are simple two-part questions about the basic facts of a disease. Look for answers to background questions in current, regularly updated electronic or print texts. Examples would be UpToDate, Clinical Evidence and ACP Medicine.
More often you will need information about:
choice of therapeutic agents,
the best diagnostic test for a disease,
or the best treatment strategy for a particular patient These types of specific questions pertain to what is referred to as foreground knowledge. Foreground questions are more complex than background questions.
Generally, analysis of foreground questions reveals four parts or components:
the patient or problem at issue;
the intervention or exposure under consideration;
a comparison intervention or exposure, when appropriate;
the clinical outcomes of interest.
Answers to these types of focused, four-component questions are in primary reports of clinical research or rigorous syntheses of them known as systematic reviews . Here you will learn the process to successfully search these resources.
Defining the question is an essential early stage in the search process. Try to divide your questions into four components:
who is affected,
what is being done,
how are effects being measured,
and, if necessary, how to compare the effectiveness of different approaches.
P atients (the "who" or the population under study),
the I nterventions/ C ointerventions or
C omparison (the "what is being done"), and the
O utcomes (the measures of how effective the interventions have been).
Use the acronym PICO to help you remember the steps. This four-part formula provides a structured approach to formatting the question and assists in identifying potential search terms.
Here is an example that includes all four components: What is the best first-line therapy for treating high blood pressure in the elderly?
Patients or Problem : Who is affected? Describe the specific patient population and/or problem context. For our question, the population is hypertensive elderly patients.
Intervention(s): What is being done? Define the interventions. We are interested in finding out which drug is the most effective monotherapy for treating hypertension in elderly people.
Comparison: How effective are different interventions? How do diuretics compare with beta-blockers or other drugs for treating the elderly with hypertension?
Outcomes Define the outcomes you wish to assess. Focus on outcomes that are important to patients like morbidity and mortality rather than intermediate surrogate endpoints like lowering blood pressure. What the patient is interested in is whether the intervention will help him/her live longer with good functional capacity and few undesirable side effects.
What Type of Question Do You Want to Ask? Clinical Map Checklist Differential Diagnosis Education Quality of Life Harm/Risk Diagnostic Tests Therapy Clinical Findings Manifestations of Disease Prevention Prognosis Cause/Etiology Cost-effectiveness
Match your clinical query to a question type . Initially, you might want to consult a checklist like the one above to help you. We can use our example, treatment of hypertension in the elderly, to demonstrate this step of the process.
Examine the different question types to clarify the main focus of interest for the clinical issue. For example, it could be Harm/Risk: Are we mainly interested in determining the side effects of this intervention? Do we need to find out if it does more harm than good?
Or maybe our interest is prevention/reduction of morbidity and mortality in our target population of hypertensive elderly patients. Alternatively, we may be concerned about cost. Is intervention a (i.e., beta-blockers) more cost-effective than intervention b (i.e., diuretics)? For the therapy question type, the focus might be examining the evidence to decide which is the most effective first line therapy for treating hypertension in the elderly. We will work with this as our question type.
Each question type may require different kinds of information for evidence and, possibly, different types of resources. We need to examine the types of information available to use as evidence and learn what kinds of studies provide this information. The Evidence Pyramid summarizes this part of the process.
Evidence Pyramid From: Medical Research Library of Brooklyn
To map the information you require to the types of research studies that will supply it, you need to become familiar with the Evidence Pyramid. It can help you to learn the types of information to use as evidence, from the strongest to the weakest, that are appropriate for your question type. For our hypertension therapy question the best evidence will be from systematic reviews of randomized controlled trials.
The Hierarchy of Evidence
Fundamental to evidence based health care is the idea of a "hierarchy of evidence". This is a model for grading the evidence. Evidence grading is based on the idea that different grades of evidence (study designs) vary in their ability to predict the effectiveness of the health practices. Higher grades of evidence are more likely to reliably predict outcomes for your patients than lower grades.
Thus, a systematic review of randomized controlled trials that show consistent results would be graded as providing higher quality evidence than a review of randomized controlled trials that show variable results without a good explanation of the variability (heterogeneity). Also, a systematic review of several randomized controlled trials provides a higher level of evidence than a single well-designed randomized controlled trial.
For a detailed description of the current revision of the Levels of Evidence and Grade of Recommendations see the new model developed at the Centre for Evidence-Based Medicine at Oxford. It is important to note that Evidence Grading deals only with the general study design - not all studies using the same general design are equally valid. Assessing the validity of a study is the objective of critical appraisal.
The Evidence Pyramid illustrates the evolution of the literature. The base of the pyramid is where information usually starts with an idea or laboratory research. As you move up the pyramid the amount of available literature decreases, but increases in relevance to the clinical setting. (McKinnell and Elliott, 1997).
High levels of evidence will not exist for all clinical questions because of the nature of medical problems and research and ethical limitations. Randomized controlled studies cannot be done in certain situations. For example, it would be unethical to measure the effect of exposure to dioxane on health by asking one group to be exposed to the chemical while another group is not exposed, since the dioxane group would be subject to unnecessary harm.
For ethical reasons, the research to answer the question would come from observational studies (cohort studies, case control studies or case series). Observational studies follow patients over time who presently have experienced the exposure/condition (for dioxane, it could be military personnel exposed to the chemical during the Viet Nam war) and compare them with another matched group without the condition or exposure.
To search for the best published studies on a clinical question, drill down the Evidence Pyramid to rapidly identify high-quality information that you can apply in clinical practice. Search appraised resources that are likely to contain reviews of the kinds of clinical research listed in the top four levels of the pyramid. It is research design studies at these levels that will most likely be clinically relevant.
For example, if you are interested in which interventions are most effective for smoking cessation, search the Cochrane Database of Systematic Reviews (CDSR) first. A simple search like 'smokers and smoking cessation' retrieved 32 relevant reviews in CDSR. If there are no systematic reviews on your question, move down to the next level of the pyramid (Randomized Controlled Double Blind Studies). Look for reviews (DARE or ACP Journal Club) of single well-designed randomized controlled trials.
If appraised resources fail to provide evidence on your question then you must search a large online medical database like MEDLINE. MEDLINE is a comprehensive database containing research studies at all levels of the pyramid and of variable quality, many having little direct application to clinical medical practice.
To construct an efficient search that will retrieve high-quality information relevant to your question you must map your question type to the appropriate study design and use a MEDLINE search filter containing terms related to the study design.
For example, the highest level of evidence for therapy questions comes from systematic reviews of randomized controlled trials (RCTs) and individual RCTs. A MEDLINE search filter might contain terms related to this type of research design – double-blind method, random allocation, randomized controlled trial (the type of publication it represents), placebos, meta-analysis, etc.
The table below links type of study or methodology to question types and then provides examples of MEDLINE search filter terms for each question type.
Evidence (Study Design) Appropriate for Question Types Matched to EBM Search Filters MEDLINE Search Filter Terms Study Design Type of Question Cohort Studies Follow-up Studies Prognosis Time Factors Morbidity Mortality Placebos Survival Analysis Disease Progression Recurrence Natural History Clinical Course Progression Observational Studies: Cohort Studies Case Control Studies Case Series Prognosis Sensitivity and Specificity Predictive Value of Tests Likelihood Functions Reproducibility of Results Cross-sectional Study: Consecutive sample design Diagnosis Double-blind Method Meta-analysis Random Allocation Clincial Trial Randomized Controlled Trial Placebo Random Systematic Reviews and Meta-Analyses Randomized Controlled Studies Therapy
MEDLINE Search Filter Terms Study Design Type of Question Randomized Controlled Trial Prevention and Control Mass Screening Sensitivity and Specificity Likelihood Functions Randomized Controlled Trials Screening Randomized Controlled Trial Prevention and Control Treatment Outcomes Clinical Trial Random Randomized Controlled Trials Prevention Case-control Studies Cohort Studies Cross-sectional Studies Risk Odds Ratio Causation Etiology or Aetiology Cohort Studies Case Control Studies Case Series Etiology/Harm
MEDLINE Search Filter Terms Study Design Type of Question McKinnell, I. and Elliott, J. (1997) The Cochrane Electronic Library: Self training guide and notes. R&D Directorate, NHS Executive Anglia and Oxford. Costs and Cost Analysis Cost-benefit Analysis Cost Control Cost Savings Cost of Illness Health Care Costs Drug Costs Hospital Costs Health Expenditures Quality Adjusted Life Year Randomized Controlled Trials Systematic Reviews Decision Analysis Model Economic Randomized Controlled Trial Practice Guidelines Outcomes Assessment (health care) Randomized Controlled Trials Quality Improvement
This is the end of Part One
Part Two will cover designing a search strategy
Part Three will cover selecting appropriate evidence resources