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Evidence-based Practice in Healthcare

This guide is designed to assist health care professionals and students become effective and efficient users of the medical literature.

Critical Appraisal

Critical appraisal is the process of carefully and systematically assessing the outcome of scientific research (evidence) to judge its trustworthiness, value and relevance in a particular context. Critical appraisal looks at the way a study is conducted and examines factors such as internal validity, generalizability and relevance.

  Some initial appraisal questions you could ask are:

  1. Is the evidence from a known, reputable source?
  2. Has the evidence been evaluated in any way? If so, how and by whom?
  3. How up-to-date is the evidence?

 Second, you look at the study itself and ask the following general appraisal questions:

  1. Is the methodology used appropriate for the researchers question? Is the aim clear?
  2. How was the outcome measured? Is that a reliable way to measure? How large was the sample size? Does the sample accurately reflect the population?
  3. Can the results be replicated?
  4. Have exclusions or limitations been listed?
  5. What implications does the study have for your practice? Is it relevant, logical?
  6. Can the results be applied to your organization/purpose?
CASP Checklists 

CASP Case Control Checklist

CASP Clinical Protection Rule Checklist

Appraisal: Validity vs. Reliability & Calculators

Appraisal is the third step in the Evidence Based Medicine process. It requires that the evidence found be evaluated for its validity and clinical usefulness. 

What is validity?

  • Internal validity is the extent to which the experiment demonstrated a cause-effect relationship between the independent and dependent variables.
  • External validity is the extent to which one may safely generalize from the sample studied to the defined target population and to other populations.

What is reliability?

Reliability is the extent to which the results of the experiment are replicable.  The research methodology should be described in detail so that the experiment could be repeated with similar results.

Statistical Calculators for Appraisal

  • Diagnostic Test Calculator
  • Risk Reduction Calculator
  • CEBM Statistics Calculator - This multi-functional tool allows you to calculate data for several different types of evidence--diagnostic tests, prospective studies, case control studies, and randomized controlled trials (RCTs).
  • Chi-Square Calculator
  • Likelihood Ratio (LR) Calculations - The LR is used to assess how good a diagnostic test is and to help in selecting an appropriate diagnostic test(s) or sequence of tests. They have advantages over sensitivity and specificity because they are less likely to change with the prevalence of the disorder, they can be calculated for several levels of the symptom/sign or test, they can be used to combine the results of multiple diagnostic test and the can be used to calculate post-test probability for a target disorder.
  • Odds Ratio - In statistics, the odds ratio (usually abbreviated "OR") is one of three main ways to quantify how strongly the presence or absence of property A is associated with the presence or absence of property B in a given population.
  • Odds Ratio to NNT Converter - To convert odds ratios to NNTs, enter a number that is > 1 or < 1 in the odds ratio textbox and a number that is not equal to 0 or 1 for the Patient's Expected Event Rate (PEER). After entering the numbers, click "Calculate" to convert the odds ratio to NNT.
  • One Factor ANOVA
  • Relative Risk Calculator - In statistics and epidemiology, relative risk or risk ratio (RR) is the ratio of the probability of an event occurring (for example, developing a disease, being injured) in an exposed group to the probability of the event occurring in a comparison, non-exposed group.
  • Two Factor ANOVA