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Sanford Library Resources - Evidence Based Practice : Evidence Based Practice - Medicine Focus

The Process of EBP

EBP provides a structure process for finding answers. The established steps to EBP are: 

1. Ask a question -convert an information need into an answerable clinical question 

2. Access the research literature - use specialized EBP resources and/or reputable databases to find the best available research evidence 

3. Appraise the research articles found - critically assess the validity and applicability of each study found 

4. Apply the research - integrate the research into practice. Combine it with patient values, circumstances and clinical expertise

5. Audit/Assess the outcomes - evaluate the effectiveness and efficiency. What might you do differently next time? 

(Straus, Glasziou, Richardson, & Hynes, 2011) 

Algorithm for Classification of Types of Clinical Research

Grimes, DA & Schulz, KF. An overview of clinical research: the lay of the land. 


Connecting a Research Question to an Appropriate Study Design

* In each case, a systematic review of all of the available studies is better than an individual study. A systematic review will compare several appropriately designed studies that have looked at the same question and aggregate the results. 

Observational Study Design

Exploratory studies are used when the state of knowledge about the phenomenon is poor; small scale, of limited duration. 

Descriptive studies (often surveys) also known as statistical research, describes data and characteristics about the population or phenomenon being studied. It does not answer questions about how/when/why the characteristics occurred, which is done under analytic research. Although the data description is factual, accurate, and systematic, the research cannot describe what caused a situation. 

Analytical studies are used to test hypotheses. I.e.: case-control, cross-sectional, cohort

Cross-Sectional Studies

Cross-Sectional Studies 

Descriptive study in which disease and exposure status are measured simultaneously in a given population. Cross-sectional studies can be though of as providing a snapshot of the frequency and characteristics of a disease in a population at a particular point in time. This type of data can be used to assess the prevalence of a acute or chronic conditions in a population. However, since exposure and disease status are measured a the same time, it may not be possible to distinguish whether the exposure preceded or followed the disease, and thus cause  and effect relationships are not certain. 

Hierarchy of Evidence Based on Study Design

Experimental Study Design - Randomized Trials

Randomized Controlled Trials 

Cohort studies where allocation to treatment and control groups is achieved by a random process. Random allocation is helpful for reducing selection bias and allocation bias, especially when combined with allocation concealment. Because they are experiments, randomized trials can employ blinding of participants and caregivers, which reduces performance bias. 

"Once Randomized, Always Analyze" 

Case Series

Clinical Case-Series are usually a coherent and consecutive set of cases of a disease (or similar problem) which derive from the fractice of one or more health care professionals or health care setting. 

Clinical case-series are of value in epidemiology for: 

  • studying predictive symptoms, signs, and tests
  • creating case definitions
  • clinical education, audit and research
  • health services research 
  • establishing safety profiles 

What to look for: 

  • the diagnosis (case definition) or, for mortality, the cause of death
  • the date when the disease or death occurred (time)
  • the place where the person lived, worked, etc. (place) 
  • the characteristics of the population (person)
  • the opportunity to collect additional data from medical records, or the person directly 
  • the size and characteristics of the population at risk

Who, what, why, when, where? 

  • Who has the disease in question?
  • What is the condition or disease being studied?
  • Why did the condition or disease arise?
  • Where does or does not the disease or condition arise? 


  • case reports and case-series can influence subsequent literature and possibly clinical practice 
  • many are followed by clinical trials 
  • often, report rare conditions for which trials may not be feasible
  • strong publication bias favoring positive results 


Cohort Study

Cohort Studies

A longitudinal observational study. It begins with a group of people who doe not have the disease, takes baseline measurements, then follows them over time using correlations to determine the absolute risk of subject contraction. 

A cohort is a group of people who share a common characteristic or experience within a defined period (i.e. are born, exposed to a drug, vaccine, pollutant, or undergo a certain medical procedure.) The comparison group may be the general population from which the cohort is drawn, or it may be another cohort of persons though to have had little or no exposure to the substance or condition under investigation, but otherwise similar. 

An example of an epidemiological question that can be answered by the use of a cohort study is: Does exposure to X (i.e. smoking) associate with outcome Y (i.e. lung cancer)? 

Such as study would recruit a group of smokers and a group of non-smokers (the unexposed group) and follow them for a set period of time and note differences in the incidence of lunch cancer between the groups at the end of the study. 

  • can be expensive 
  • convenient for studying many diseases 
  • can calculate incidence rates or risks and their differences and ratios  

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