1 Important points to consider when critically evaluating published research papers

Simple review articles (also referred to as ‘narrative’ or ‘selective’ reviews), systematic reviews and meta-analyses provide rapid overviews and ‘snapshots’ of progress made within a field, summarising a given topic or research area. They can serve as useful guides, or as current and comprehensive ‘sources’ of information, and can act as a point of reference to relevant primary research studies within a given scientific area. Narrative or systematic reviews are often used as a first step towards a more detailed investigation of a topic or a specific enquiry (a hypothesis or research question), or to establish critical awareness of a rapidly-moving field (you will be required to demonstrate this as part of an assignment, an essay or a dissertation at postgraduate level).

The majority of primary ‘empirical’ research papers essentially follow the same structure (abbreviated here as IMRAD). There is a section on Introduction, followed by the Methods, then the Results, which includes figures and tables showing data described in the paper, and a Discussion. The paper typically ends with a Conclusion, and References and Acknowledgements sections.

The Title of the paper provides a concise first impression. The Abstract follows the basic structure of the extended article. It provides an ‘accessible’ and concise summary of the aims, methods, results and conclusions. The Introduction provides useful background information and context, and typically outlines the aims and objectives of the study. The Abstract can serve as a useful summary of the paper, presenting the purpose, scope and major findings. However, simply reading the abstract alone is not a substitute for critically reading the whole article. To really get a good understanding and to be able to critically evaluate a research study, it is necessary to read on.

While most research papers follow the above format, variations do exist. For example, the results and discussion sections may be combined. In some journals the materials and methods may follow the discussion, and in two of the most widely read journals, Science and Nature, the format does vary from the above due to restrictions on the length of articles. In addition, there may be supporting documents that accompany a paper, including supplementary materials such as supporting data, tables, figures, videos and so on. There may also be commentaries or editorials associated with a topical research paper, which provide an overview or critique of the study being presented.

There are various strategies used in reading a scientific research paper, and one of these is to start with the title and the abstract, then look at the figures and tables, and move on to the introduction, before turning to the results and discussion, and finally, interrogating the methods.

Another strategy (outlined below) is to begin with the abstract and then the discussion, take a look at the methods, and then the results section (including any relevant tables and figures), before moving on to look more closely at the discussion and, finally, the conclusion. You should choose a strategy that works best for you. However, asking the ‘right’ questions is a central feature of critical appraisal, as with any enquiry, so where should you begin? Here are some critical questions to consider when evaluating a research paper.

Look at the Abstract and then the Discussion: Are these accessible and of general relevance or are they detailed, with far-reaching conclusions? Is it clear why the study was undertaken? Why are the conclusions important? Does the study add anything new to current knowledge and understanding? The reasons why a particular study design or statistical method were chosen should also be clear from reading a research paper. What is the research question being asked? Does the study test a stated hypothesis? Is the design of the study appropriate to the research question? Have the authors considered the limitations of their study and have they discussed these in context?

Take a look at the Methods: Were there any practical difficulties that could have compromised the study or its implementation? Were these considered in the protocol? Were there any missing values and, if so, was the number of missing values too large to permit meaningful analysis? Was the number of samples (cases or participants) too small to establish meaningful significance? Do the study methods address key potential sources of bias? Were suitable ‘controls’ included in the study? If controls are missing or not appropriate to the study design, we cannot be confident that the results really show what is happening in an experiment. Were the statistical analyses appropriate and applied correctly? Do the authors point out the limitations of methods or tests used? Were the methods referenced and described in sufficient detail for others to repeat or extend the study?

Take a look at the Results section and relevant tables and figures: Is there a clear statement of findings? Were the results expected? Do they make sense? What data supports them? Do the tables and figures clearly describe the data (highlighting trends etc.)? Try to distinguish between what the data show and what the authors say they show (i.e. their interpretation).

Moving on to look in greater depth at the Discussion and Conclusion: Are the results discussed in relation to similar (previous) studies? Do the authors indulge in excessive speculation? Are limitations of the study adequately addressed? Were the objectives of the study met and the hypothesis supported or refuted (and is a clear explanation provided)? Does the data support the authors’ conclusions? Maybe there is only one experiment to support a point. More often, several different experiments or approaches combine to support a particular conclusion. A rule of thumb here is that if multiple approaches and multiple lines of evidence from different directions are presented, and all point to the same conclusion, then the conclusions are more credible. But do question all assumptions. Identify any implicit or hidden assumptions that the authors may have used when interpreting their data. Be wary of data that is mixed up with interpretation and speculation! Remember, just because it is published, does not mean that it is right.

Other points you should consider when evaluating a research paper: Are there any financial, ethical or other conflicts of interest associated with the study, its authors and sponsors? Are there ethical concerns with the study itself? Looking at the references, consider if the authors have preferentially cited their own previous publications (i.e. needlessly), and whether the list of references are recent (ensuring that the analysis is up-to-date). Finally, from a practical perspective, you should move beyond the text of a research paper, talk to your peers about it, consult available commentaries, online links to references and other external sources to help clarify any aspects you don’t understand.

The above can be taken as a general guide to help you begin to critically evaluate a scientific research paper, but only in the broadest sense. Do bear in mind that the way that research evidence is critiqued will also differ slightly according to the type of study being appraised, whether observational or experimental, and each study will have additional aspects that would need to be evaluated separately. For criteria recommended for the evaluation of qualitative research papers, see the article by Mildred Blaxter (1996), available online. Details are in the References.