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Evidence Based Medicine and Epidemiology

Evidence Based Medicine: Definition and Purpose

  • Evidence Based Medicine (EBM) is defined as “the conscientious, explicit and judicious use of current best evidence in making decisions about the care of individual patients” (Cocharne.org). It is also known as evidence-based practice.
  • There will be ANCC exam questions testing your ability to sort and rate articles by the level of evidence.
  • Rationale: Use the best available evidence to inform patient care, integrating clinical expertise with patient values and preferences.

Hierarchy of Research Evidence

  • Meta-analysis
    • Statistical method that combines data from multiple studies (systematic reviews).
    • Results in higher statistical power and a single conclusion.
    • Gold standard for evaluating research evidence in EBM.
  • Systematic review
    • Identifies, selects, and analyzes multiple research articles on a health condition or practice.
    • Follows explicit methodology to identify all relevant studies.
    • Included studies meet explicit criteria.
    • Studies are ranked from grade A (best) to grade D (poor).
    • After identifying acceptable studies, data are pooled and subjected to meta-analysis.
  • Randomized controlled trial (RCT)
    • Subjects are randomly assigned to a control group or one or more treatment groups.
    • Intervention can be a drug, procedure, or device.
    • Some RCTs use a double-blind design (intervention hidden from patient, clinician, and/or researchers).
    • RCTs are experimental studies.
  • Experimental study
    • Involves random subject selection, one placebo/control group, and one or more intervention groups.
    • An RCT is a type of experimental study.
  • Cohort study
    • Used to investigate risk factors for diseases, death, and other conditions.
    • Subjects are observed over a long period; no intervention is performed (not an experiment).
    • Goal is to identify risk factors and associations (not causation).
    • Example: Nurses’ Health Study – large cohort of female RNs aged 30–63 in Massachusetts.
    • A cohort study can be prospective (present to future).
  • Case report
    • Detailed report of one patient with a disease or unusual condition including demographics, signs/symptoms, diagnosis, and response to treatment.
  • Case series
    • Series of case reports involving multiple individuals treated similarly.
  • Opinions and editorials
    • Can be biased and may not be based on solid evidence; considered the weakest form of evidence.

Study Designs: Key Points and Real-World Relevance

  • RCTs are the strongest experimental design for establishing causality.
  • Systematic reviews and meta-analyses synthesize evidence across many studies to provide robust conclusions.
  • Observational studies (cohort, case-control, cross-sectional) identify associations and risk factors but are more limited in proving causation.
  • In clinical practice, decisions are often guided by the hierarchy of evidence, balancing study quality with applicability to the patient.

Research Databases

  • Cochrane Reviews
    • Gold standard database/resource for EBM (Cochrane Database of Systematic Reviews).
    • Produced by the Cochrane Collaboration.
    • The organization does not accept commercial or conflicted funding.
  • Medline®
    • The U.S. National Library of Medicine’s premier bibliographic database.
    • Contains more than 26{,}000{,}000 journal articles in the life sciences.
    • Covers 5{,}200 current biomedical journals globally.
    • PubMed® is a component of Medline and contains more than 30{,}000{,}000 citations and abstracts.
  • CINAHL
    • The world’s largest source of full-text nursing and allied health journals (>1{,}300 journals).
    • Provides indexing of more than 4{,}000 journals.

Grades of Research Evidence

  • Evidence is assigned a letter grade: A (best), B, C, D (poor).
  • Well-designed controlled experimental trials (double-blind RCTs) are considered Grade A (Level 1) evidence.

Statistical Terms (Evidence Based Medicine)

  • Confidence Interval (CI)
    • A measure of the degree of certainty in a sampling method.
    • Example: A 95\% CI is a range of values that you can be 95\% certain contains the true mean of the population.
    • General expression for a mean: CI = \bar{x} \pm z_{0.975} \cdot \frac{s}{\sqrt{n}} for a 95% CI.
  • Absolute Risk Reduction (ARR)
    • Defined as the difference in risk between two treatments for a given outcome.
    • Formula: ARR = E{control} - E{treatment} where E denotes event probability.
  • Relative Risk Reduction (RRR)
    • How much risk is reduced in the experimental group compared with the control group.
    • Formula: RRR = \frac{E{control} - E{treatment}}{E{control}} = 1 - \frac{E{treatment}}{E_{control}}

Additional Clinical Effectiveness Metrics

  • Number Needed to Treat (NNT)
    • The number of patients you must treat to prevent one additional bad outcome (e.g., MI, stroke).
    • Example: An NNT of 7 means that seven patients need to be treated to avoid one bad outcome.
    • Formula: NNT = \frac{1}{ARR} = \frac{1}{E{control} - E{treatment}}
  • Predictive Values
    • Positive Predictive Value (PPV): Probability that a person with a positive screening test has the disease.
    • Formula: PPV = \frac{TP}{TP + FP}
    • Negative Predictive Value (NPV): Probability that a person with a negative screening test does not have the disease.
    • Formula: NPV = \frac{TN}{TN + FN}
      where TP = true positives, FP = false positives, TN = true negatives, FN = false negatives.

Epidemiology Terms

  • Active immunity
    • Immunity developed through vaccination or infection.
  • Passive immunity
    • Immunity acquired by receiving antibodies (immunoglobulins) from another host.
    • Example: Colostrum from breastfeeding provides neonate antibodies from the mother.
  • Herd immunity
    • Resistance to a disease in a large portion of the population, typically due to immunization programs.
  • Health
    • A state of complete physical, mental, and social well-being.
  • Horizontal transmission
    • Transmission of an infectious agent from one individual to another.
    • Example: HIV and other sexually transmitted infections transmitted through sexual intercourse.
  • Vertical transmission
    • Transmission of an infectious agent from mother to infant.
    • Congenital infections passed from mother to infant; HIV-positive mothers may transmit via breastmilk (vertical transmission).
  • Endemic
    • A baseline level of a disease in a population.
  • Epidemic
    • Rapid increase of a disease in a population affecting a large number of people.
  • Pandemic
    • An epidemic that occurs over a very large area (several countries or continents), involving a large proportion of the global population.
  • Morbidity
    • Illness or departure from physical/mental health.
  • Mortality
    • Death.
  • Infant mortality
    • Infant deaths per 100,000 live births.
    • Leading cause of death in the infant’s first year is congenital malformations (including chromosomal abnormalities).
  • Sensitivity
    • Ability of a screening test to correctly identify a person with the disease.
  • Specificity
    • Ability of a screening test to correctly identify a person without the disease.