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 1) you should not cite papers that don’t directly pertain
to the research you plan to describe; 2) 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; and 3) 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.
Example
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.
Checklist 1. Minimum amount of background required to understand “the problem”/hypotheses 2. Clearly framed “problem”/hypotheses 3. Balanced and current literature cited 4. Technical and non-familiar terms clearly defined 5. Brief description of what was done and what was achieved in the final paragraph