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Stony Brook University

Evaluating Evidence

This guide contains information on risk of bias tools, critical appraisal, external and internal validity.

Definitions

Validity - Did you follow scientific methods to find the results? Are there systematic errors?

Internal validity - when a study is free from bias or the extent to which the observed effects are true for people in a study. (Cochrane)

External validity - when a study is generalizable or applicable. How applicable are the results to the target population? 

Reliability - How consistent are the results? Can you get consistent results each time you rerun the study?

Relevance - How applicable is this to your patient?

Types of Bias

Internal Validity may be affected by these types of bias:

  • Allocation bias
  • Confounding
  • Blinding
  • Data Collection methods
  • Withdrawals/dropouts
  • Statistical analysis
  • Intervention integrity/contamination 

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