Introduction to Critical Appraisal by Michelle Maden

What is Critical Appraisal?

Critical Appraisal is an assessment of the strengths and weaknesses of research methodology. It aims to examine bias and assess both internal validity and external validity

  • Bias – Systematic error in individual studies that can lead to erroneous conclusions (e.g. an overestimation or underestimation of the true result).
  • Internal validity – The extent to which the design and conduct of a study are likely to have prevented bias, and therefore, the results may be considered reliable. It is concerned with intrinsic factors.
  • External validity – The extent to which the results of a study might be expected to occur in other participants/settings (generalisability). It is concerned with extrinsic factors.


Critical appraisal is:

  • A balanced assessment of the benefits/strengths and flaws/weaknesses of a study
  • An assessment of research process and results
  • Consideration of quantitative and qualitative aspects


Critical appraisal is not:

  • Negative dismissal of any piece of research
  • Assessment on results alone
  • Based entirely on statistical analysis
  • Undertaken by experts only


Critical appraisal is a holistic process which involved an examination of both the methods and the results. It allows more emphasis on intrinsic factors (how well the study was put together) than extrinsic factors (who wrote it and where it came from) and encourages the reader not to accept the findings at face value but give them the confidence to accept or reject them.


What do you need to know?

  • Bias in research designs
  • Tools/resources for critical appraisal


…What about statistics?

It helps to be able to interpret the statistics in the paper, but you don’t necessarily need to know how to calculate them! For those new to critical appraisal, choose papers or research designs that do not report statistics in them (e.g. qualitative).


Tools for critical appraisal

CATNiP – Critical Appraisal Toolkit Navigating into Practice

See our Aintree Library webpages for more resources


 Michelle Maden
Aintree Library & Information Resource Centre

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