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Evidence-Based Practice: Appraise the Evidence

Evidence-Based Practice Help Guide

Appraise the Evidence

Critical analysis is a way or examining the research to assess its validity and relevance. It is an essential step in making sense of the research evidence. You should ask the following questions:

  • What are the key terms and concepts?
  • Importance of the research question being answered
  • How relevant is this article to my specific question?
  • Strengths and weaknesses of the articles study design and methodology
  • How authoritative and credible is this source?
  • Any potential conflicts of interest
  • Legitimacy of conclusions

Critical Appraisal Tools

Below is a list of critical appraisal tools used in evidence-based medicine:

Understanding Terminology

The following terminology is important in critical appraisal and will be helpful to determine the validity of research. Additianal terms can be found in the Centre for Evidence Based Medicine Glossary 


Whether a particular treatment or form of care that was demonstrated as effective in a trial could be expected to provide the same effect for an individual or group in a specific clinical or population setting


Any influence that may cause a distortion of results in a study and undermine validity. Bias may originate from various sources, such as allocation of patients, measurement, interpretation, publication, and review of data

Confidence interval (CI)     

Confidence Interval (CI) is the interval within which the population parameter (the ‘true’ value) is expected to lie with a given degree of certainty, for example 95%

External validity

External validity is the degree to which the results of a clinical study can be applied to a setting  other than the one studied.


The ability to reliably apply the results of a study to other populations, based on the characteristics of the subjects, size of the sample, the setting, and trustworthiness of the study


A method of analysis for randomized trials in which all patients randomly assigned to one of the treatment groups is analysed with that assigned group, regardless of whether or not they completed or received the treatment.

Internal validity        

A study has internal validity if it is free from bias or systematic error and the results seen are due only to the intervention.

p value

p value is the probability that a particular result would have happened by chance.


   Ability to detect a difference between two experimental groups if a difference exists.

Relative risk (RR)

Relative Risk (RR) is the ratio of the probability of outcome in the treatment and control groups. This expresses the risk of the probable outcome in the treatment group relative to that in the control group.


The extent of the measurement of trustworthiness of the results.

YouTube - Appraising Evidence





Learn more about




Confidence Intervals & p values

Confidence Intervals and p values, published by Hayward Medical Communication

Numbers needed to treat

Numbers needed to treat, BMJ 2010; 341

How to calculate numbers needed to treat (YouTube 3:48)

Relative risk

How to calculate relative risk (YouTube 3:14)

Odds ratios

Odds and odds ratios, BMJ 2013; 347

How to calculate an odds ratio (YouTube 3:17)

Intention to treat

Intention-to-treat analysis, BMJ 2013; 346

Intention to treat analysis - what is it and why is it important (YouTube 4:43)

Forest plots

How to read a forest plot in a meta-analysis, BMJ 2015; 351

How to interpret a forest plot (YouTube 5:32)