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Evidence Based Dentistry (EBD)

Systematic Reviews and Meta-Analyses

Systematic Review - a comprehensive survey of a topic in which all of the primary studies of the highest level of evidence  have been systematically identified, appraised and then summarized according to an explicit and reproducible methodology.

  • Narrow scope
  • —Focus -  answering specific questions
  • —Discusses key findings & interprets the results
  • —Critical analysis of the included studies

Meta-Analysis – a survey in which the results of all of the included studies are similar enough statistically that the results are combined and analyzed as if they were one study.

  • —Statistical process commonly used with systematic reviews
  • —Combine the data from multiple individual studies into one analysis
  • —Can provide statistical power for small SRs
  • There can be  Meta-Analyses of studies other than SRs 


Know the difference between Systematic Reviews and other kinds of review articles

Narrative Reviews

  • —Broad focus on a topic.
  • —Can provide an overall picture of the available literature on a topic.
  • —Describes the outcomes of studies – but does not review the study design.

Critical Summaries

  • Produced by evidence based journals.
  • —Provide easy-to-read critical summaries of original and review articles.
  • —Can help the practitioner stay up to date.

Randomized Controlled Studies

Randomized Controlled Studies

  • Randomly assign subjects to either experimental or control group.
  • There are two groups, one treatment group and one control group. The treatment group receives the treatment under investigation, and the control group receives either no treatment or some standard default treatment.
  • Provides strongest evidence for demonstrating cause & effect.
  • RCTs are the standard method of answering questions about the effectiveness of different therapies. 
  • Can use blind or double blind strategies.


—Nonrandomized Controlled Study
  • Often rely on historical controls - less confidence in findings
  • Used to screen new therapies – should they be tested in a randomized study?
  • Used in diagnostic studies – new test compared to a gold standard test

Cohort Studies

Cohort Study - patients who presently have a certain condition and/or receive a particular treatment are followed over time and compared with another group who are not affected by the condition under investigation.

  • Subjects do NOT have the condition of interest.
  • Researcher DOES NOT give a treatment, intervention, or provide an exposure – no attempt to control variables.
  • Observe the association between a risk factor and subsequent development of a disease.
  • Followed over time to when/if they develop the condition.

Case Control Studies

Case Control Studies - patients who already have a certain condition are compared with people who do not.

  • Make observations about possible associations between a disease and one or more hypothesize risk factors.
  • Retrospective – subjects already have the disease.
  • Comparison made with a representative group of disease-free people.

Case Series and Case Reports

Case Series and Case Reports - consist either of collections of reports on the treatment of individual patients, or of reports on a single patient.

  • Report treatments on several or a single patient.
  • Useful if a patient presents with a condition a clinician has never seen or heard of before.
  • No statistical validity.
  • Important in identifying new health concerns – e.g., toxic shock syndrome,  AIDS.