Setting the scene
The introduction must provide the reader with sufficient background information for them to put your work into context. It needn’t and shouldn’t be a comprehensive literature review of the field: that is what review articles are for. Instead, it should present “the problem,” basically whatever the research question is, thereby defining the rationale for the study. The introduction should also briefly explain how you addressed this problem and what was achieved. Put another way, it should be clear from the introduction what related work has been done before, why the current study was performed, what you did, and what you found.
A comprehensive literature search should have been performed before launching into your study. If not, you run the risk that someone has previously done what you intend to do. However, it is also possible that similar or related studies are published during the several months it takes to perform the research. Therefore, the literature should be reviewed on an on-going basis to ensure that you are up to date with all developments in your field of research. As with all references to the literature, the literature cited in the introduction needs to be current, balanced and relevant.
What this means is that:
- You should not cite papers that don’t directly pertain to the research you plan to describe
- You must cite all relevant papers, not only your own research and papers that support your hypothesis, but also papers that contradict your findings or propose alternative ideas
- Only the most recent papers showing a particular finding should be cited, unless referring to an older paper to explain the evolution of thought in the field or the development of a particular method
The minimum amount of background for a reader to understand the rationale for your study is all that is required. If a reader wants to know more they will find a review on the subject; indeed, many authors refer readers to review articles for additional information, thereby reducing the length of their introduction.
It is usually a good idea to briefly describe what was done and what was found at the end of the introduction, but it is important not to go into too much detail or you will end up repeating what is already described in the methods and results sections. A sentence or two for each is usually sufficient.
Finally, any non-standard abbreviations, technical terms and terms that might be unfamiliar to some readers should be clearly defined in the introduction. For example, in a paper describing research on Leishmania major, it would not be helpful (or appreciated by the reader) if it was left until the discussion to mention that this is a protozoan parasite responsible for the skin disease leishmaniasis. Similarly, in a paper describing findings relating to the protein BCL-10, the fact that it has been shown to induce apoptosis and activate the signaling molecule NF-κB should be mentioned in the introduction rather than being left until the discussion.
In the example above, published in The Journal of Clinical Investigation (doi:10.1172/JCT38289; reproduced with permission), the authors clearly state what the problem is and follow this with five paragraphs of background (not shown) explaining the results of previous work and their implications. This leads nicely to the rationale for the study, which is logically followed by a description of what was done in the present study. The authors of this paper chose not to mention their findings in the introduction, possibly because the description of what was done was quite detailed, but most likely because the results section immediately follows the introduction in JCI papers, with the Methods coming after the Discussion section.
- Minimum amount of background required to understand “the problem”/hypotheses
- Clearly framed “problem”/hypotheses
- Balanced and current literature cited
- Technical and non-familiar terms clearly defined
- Brief description of what was done and what was achieved in the final paragraph