2.4 Critically Appraising the Literature

Faith Alele and Bunmi Malau-Aduli

Now that you have explored the parts of a research paper, we will discuss how to critically appraise a paper in the section below.

Critical appraisal refers to the process of carefully and methodically reviewing research to determine its credibility, usefulness, and applicability in a certain context.6 It is an essential element of evidence-based practice.

As stated earlier, you want to ensure that what you read in the literature is trustworthy before considering applying the findings in practice. The key things to consider include the study’s results, if the results match the conclusion (validity) and if the findings will help you in practice (applicability). A stepwise approach to reading and analysing the paper is a good way to highlight important points in the paper. While there are numerous checklists for critical appraisal, we have provided a simple guide for critical appraisal of quantitative and qualitative studies. The guides were adapted from Epidemiology by Petra Buttner (2015) and How to Read a Paper [the basics of evidence-based medicine and healthcare (2019);  papers that go beyond numbers- qualitative research (1997)] by Trisha Greenhalgh to aid your review of the papers.5,7,8

A guide to reading scientific articles – Quantitative studies

What is the title of the study?

  • Does the title clearly describe the study focus?
  • Does it contain details about the population and the study design?

What was the purpose of the study (why was it performed)?

  • Identify the research question
  • Identify the exposure and outcome

What was the study design?

  • Was the design appropriate for the study?

Describe the study population (sample)

  • What was the sample size?
  • How were participants recruited?
  • Where did the research take place?
  • Who was included, and who was excluded?
  • Are there any potential sources of bias related to the choice of the sample?

What were data collection methods used?

  • How were the exposure and outcome variables were measured
  • How was data collected- instruments or equipment? Were the tools appropriate?
  • Is there evidence of random selection as opposed to systematic or self-selection?
  • How was bias minimised or avoided?

For experimental studies

  •  How were subjects assigned to treatment or intervention: randomly or by some other method?
  •  What control groups were included (placebo, untreated controls, both or neither)
  •  How were the treatments compared?
  •  Were there dropouts or loss to follow-up?
  •  Were the outcomes or effects measured objectively?

For observational studies

  • Was the data collection process adequate (including questionnaire design and pre-testing)?
  • What techniques were used to handle non-response and/or incomplete data?
  •  If a cohort study, was the follow-up rate sufficiently high?
  •  If a case-control study, are the controls appropriate and adequately matched?

How was the data analysed?

  • Is the statistical analysis appropriate, and is it presented in sufficient detail?

What are the findings?

  • What are the main findings of the study? Pay specific attention to the presented text and tables in relation to the study’s main findings.
  • Are the numbers consistent? Is the entire sample accounted for?

Experimental study

  •  Do the authors find a difference between the treatment and control groups?
  •  Are the results statistically significant? If there is a statistically significant difference, is it enough of a difference to be clinically significant?

Observational study

  •  Did the authors find a difference between exposed and control groups or cases and controls?
  •  Is there a statistically significant difference between groups?
  •  Could the results be of public health significance, even though the difference is not statistically significant? (This may highlight the need for a larger study).
  • Are the results likely to be affected by confounding? Why or why not?
  • What (if any) variables are identified as potential confounders in the study?
  • How is confounding dealt with in this study?
  • Are there any potential confounders that the authors have not taken into account? What might the likely impact be on the results?

Reading and Activity

Read the following article:

Chen X, Jiang X, Huang X, He H, Zheng J: Association between probiotic yogurt intake and gestational diabetes mellitus: a case-control study. Iran J Public Health. 2019, 48:1248-1256.

Activity 1️⃣⏰30 Minutes

After reading the article above, let’s now conduct a critical appraisal of the article.

A guide to reading scientific articles – Qualitative studies

What is the title of the study?

  • Does the title clearly describe the study focus?
  • Does it contain details about the population and the study design?

What is the research question?

Was a qualitative approach appropriate?

  • Identify the study design and if it was appropriate for the research question.

How were the setting and the subjects selected?

  • What sampling strategy was used?
  • How were participants recruited?
  • Where was the study conducted?

Was the sampling strategy appropriate for the approach?

  • Consider the qualitative approach used and decide if the sampling strategy or technique is appropriate

What was the researcher’s position, and has this been taken into account?

  • Consider the researcher’s background, gender, knowledge, personal experience and relationship with participants

What were the data collection methods?

  • How was data collected? What technique was used?

How were data analysed, and how were these checked?

  • How did the authors analyse the data? Was this stated?
  • Did two or more researchers conduct the analysis independently, and were the outcomes compared (double coding)?
  • Did the researchers come to a consensus, and how were disagreements handled?

Are the results credible?

  • Does the result answer the research question?
  • Are themes presented with quotes and do they relate to the research question or aim?

Are the conclusions justified by the results?

  • Have the findings been discussed in relation to existing theory and previous research?
  • How well does the interpretation of the findings fit well with what is already known?

Are the findings transferable to other settings?

  • Can the findings be applied to other settings? Consider the sample.

Reading and Activity

Now that you know how to critically appraise both quantitative and qualitative papers, it is also important to note that numerous critical appraisal tools exist. Some have different sub-tools for different study designs, while others are designed to be used for multiple study designs. These tools aid the critical appraisal process as they contain different questions to prompt the reader while assessing the study’s quality.9

Examples of tools commonly used in health professions are listed below in Table 2.2. Please note that this list is not exhaustive, as numerous appraisal tools exist. You can use any of these tools to appraise the quality of an article before choosing to use their findings to inform your own research or to change practice.

Table 2.2 Critical appraisal tools
Tool name Type of Research Website
Critical Appraisal Skills Programme (CAS) (UK) Quantitative, Qualitative, Systematic Reviews, Economic evaluation https://casp-uk.net/casp-tools-checklists/
CEBM (Oxford’s Centre for Evidence Based Medicine Systematic Reviews, Diagnostic Accuracy Studies, Prognosis Studies, Randomised Controlled Trials (RCT), Qualitative Studies, Individual Patient Data Reviews https://www.cebm.ox.ac.uk/resources/ebm-tools/critical-appraisal-tools
PEDro Scale (Physiotherapy evidence database) Randomised Controlled trials only https://pedro.org.au/english/resources/pedro-scale
Joanna Briggs Institute (JBI) Critical Appraisal Tools Quantitative, qualitative, economic evaluation, systematic reviews https://jbi.global/critical-appraisal-tools
CanChild/McMaster EBP Research Group-Evidence Review Forms Quantitative and Qualitative https://canchild.ca/en/resources/137-critical-review-forms-and-guidelines
Mixed Methods Appraisal Tool Systematic mixed studies reviews (reviews including original qualitative, quantitative and mixed methods studies) http://mixedmethodsappraisaltoolpublic.pbworks.com/w/page/24607821/FrontPage
AMSTAR 2 Systematic reviews that include randomised or non-randomised studies of healthcare interventions https://amstar.ca/Amstar-2.php
QUADAS-2 Diagnostic accuracy studies https://www.acpjournals.org/doi/full/10.7326/0003-4819-155-8-201110180-00009?rfr_dat=cr_pub++0pubmed&url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org

Additional Reading

  1. How to read a paper: The Medline database BMJ 1997; 315 doi: https://doi.org/10.1136/bmj.315.7101.180 (Published 19 July 1997) Cite this as: BMJ 1997;315:180
  2. How to read a paper : Getting your bearings (deciding what the paper is about) BMJ 1997; 315 doi: https://doi.org/10.1136/bmj.315.7102.243 (Published 26 July 1997) Cite this as: BMJ 1997;315:243
  3. How to read a paper: Assessing the methodological quality of published papers BMJ 1997; 315 doi: https://doi.org/10.1136/bmj.315.7103.305 (Published 02 August 1997) Cite this as: BMJ 1997;315:305
  4. How to read a paper: Papers that summarise other papers (systematic reviews and meta-analyses) BMJ 1997; 315 doi: https://doi.org/10.1136/bmj.315.7109.672 (Published 13 September 1997) Cite this as: BMJ 1997;315:672
  5. How to read a paper: Papers that go beyond numbers (qualitative research) BMJ 1997; 315 doi: https://doi.org/10.1136/bmj.315.7110.740 (Published 20 September 1997) Cite this as: BMJ 1997;315:740
  6. How to read a paper: Papers that tell you what things cost (economic analyses)BMJ 1997; 315 doi: https://doi.org/10.1136/bmj.315.7108.596 (Published 06 September 1997) Cite this as: BMJ 1997;315:596
  7. How to read a paper: Papers that report diagnostic or screening tests BMJ 1997; 315 doi: https://doi.org/10.1136/bmj.315.7107.540 (Published 30 August 1997) Cite this as: BMJ 1997;315:540
  8. How to read a paper: Papers that report drug trials BMJ 1997; 315 doi: https://doi.org/10.1136/bmj.315.7106.480 (Published 23 August 1997) Cite this as: BMJ 1997;315:480
  9. How to read a paper: Statistics for the non-statistician. I: Different types of data need different statistical tests BMJ 1997; 315 doi: https://doi.org/10.1136/bmj.315.7104.364 (Published 09 August 1997) Cite this as: BMJ 1997;315:36
  10. How to read a paper: Statistics for the non-statistician. II: “Significant” relations and their pitfalls BMJ 1997; 315 doi: https://doi.org/10.1136/bmj.315.7105.422 (Published 16 August 1997) Cite this as: BMJ 1997;315:422
Activity 3️⃣⏰90 Minutes

In the additional reading above there are key readings worth exploring and summarising for future reference.  Readings 2,3,5, 9 and 10 are suggested and others are there for your interest.  Complete the activity below using the recommended readings above and the others are linked for your exploration.


Chapter Attribution

Alele, F., & Malau-Aduli, B. (2023). An introduction to research methods for undergraduate health profession students. James Cook University. https://jcu.pressbooks.pub/intro-res-methods-health

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