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What are critical appraisal skills?
These skills allow you to decide, when you are reading a research article,
Whether the study is well designed and whether you can apply it to your practice.
In other words,
“To weigh up the evidence critically, to assess its validity and usefulness.” Sackett (2000)
Critical appraisal skills enable you to:
- Identify poor quality research
- Identify poorly reported research
- Concentrate your reading time on better quality articles
- Discuss critically with patients any published material about their condition which they find and ask you about
Why do you need to develop skills in critical appraisal?
Basing your clinical practice on good quality evidence is becoming increasingly important. But you can not simply take everything you read at face value.
Even articles published in reputable journals can be flawed. They may report research which is not relevant, or there may be errors in the research design which mean you cannot rely on the information given to change your practice.
This article (login with your NHS Athens account) explains how research papers often contain methodological errors, report results selectively, and draw unjustified conclusions; a review of 308 phase 2 trials in cancer (295 of which were single-arm studies) found that 250 (81%) did not report an identifiable statistical design.
How Does this Work In Practice?
For a demonstration of the key points of the critical appraisal process, let’s look at an example.
You are Head of Occupational Health at a large call centre. You are worried about the health of your employees, especially as their jobs involve sitting at workstations all day. They get little exercise and you feel they could have problems with obesity in the future. Your Chief Executive tells you he has heard about an exciting new treadmill people can use while working at a computer. He wants to order some tomorrow and asks you how many he should buy. Read this article and tell him whether the researchers have proved that the treadmill is effective. This video will help you consider the key points within the article
Now that we have seen the principles of critical appraisal let’s look at statistics in more detail, using the let’s look at a clinical paper reporting on a randomised controlled trial.
Critical Appraisal: statistics and results
Results are expressed in different ways using statistics in research articles. For example, statistics you will often see are –
Number needed to treat
For definitions of these terms, click HERE.
Let’s put this into context:
You have been told by your doctor that you need to reduce your cholesterol. Which of the following interventions would you choose to help to reduce your cholesterol?
1. An intervention which reduces your risk of having high cholesterol by 75%
2. An intervention which has an absolute risk reduction of 30%
3. An intervention which reduces your chances of having high cholesterol from 40% to 10%
4. A scheme which needs 3 people to take part to prevent one additional person from having high cholesterol
Intervention 1 looks by far the most impressive. However all of these statistics are different ways of expressing the same results! The figure used in Intervention 1 is a relative risk.
Be aware when reading papers that relative risks can be misleading as they can make the results appear more striking.
Now let’s see how to work out these figures, using this fictional trial.
Try out your skills:
We looked above at an article – Randomised controlled trial of specialist nurse intervention in heart failure (click HERE for the full article). Now let’s focus on the statistics used in this paper.
Congratulations! You now have the skills to critically appraise clinical papers. Now think about how you will maintain these skills and how you can use them to make your practice more evidence based.
How The Library Can Help With Critical Appraisal?
Critical appraisal training
Library Services can provide training on critical appraisal to Trust staff. We offer an interactive half day training session where we read a paper and decide how valid the results really are. If you would like us to visit your department or journal club, please Contact Us
To read more about critical appraisal try one of these books from the Trust Libraries
Lancashire and South Cumbria Library Service have a very useful webpage linking to several tools for critical appraisal
- CASP checklists
- CEBM critical appraisal tools
- BestBETs worksheets for the critical appraisal of different study types
Sackett, D.L, (2000) Evidence Based Medicine, Churchill Livingstone.