How to write #3- The introduction

The nature of the problem

Almost everyone who works in science struggles with writing. The natural skills that earn us careers in science, such as observation or technical abilities tend to leave us disadvantaged relative to those with a flair for the arts or languages. There are also many aspects in the way we are trained that don’t equip us for something that (at least in academia) we end up doing on a daily basis. Most young scientists don’t perfect the art of writing until they have written a PhD thesis, but that particular writing exercise leaves them ill-equipped for writing papers. The thesis rewards excessive length and detail, whilst the scientific paper requires brevity. At the early stages of our writing careers we are not trained to deal with this format. Thesis writing, or producing undergraduate essays instills the instinct is to write a full review of the literature when we tackle the introduction to a paper. We forget that this element of the research article is not about showing how clever and knowledgeable we are. Before you start to write you need to accept that editors and reviewers don’t like long introductions and producing one could be a last straw prompting rejection, or at the very least will result in some annoying revisions.

What the introduction is for

Hopefully the paragraph above spells out what the introduction isn’t for. It is not a literature review. The introduction to a paper has one simple function, which is to presents the rationale for the work described in the paper. It should be short and provide a brief account of the landmark studies that got the field to where it is, what is currently known and what are the unanswered questions. The introduction gives an indication of what are you going to be presenting in the main body of the text. Above all this section of the paper should spell out why this work was important, why it is timely and why your readers should be interested in reading any further.


Where should we start?

It took me a while to work this out for myself, as it is counter-intuitive. Just as we don’t actually start writing the paper by doing the abstract, then the introduction, then the methods, etc (I actually suggest you start with the results section), we don’t start writing the introduction with the beginning. The best way of tackling this section of the paper is to start at the end, in fact with the very last lines. This will generally be the statement or statements of intent for the paper. You set out clearly what you were trying to achieve when you did your research. Not all research is hypothesis driven, but if yours is, then your hypothesis should be stated at the end of your introduction. Where there is no hypothesis you will still have had aims or objectives when you began your project, so end the introduction with those. At the end of your introduction the reader should be in no doubt about what you were trying to achieve. In some disciplines common to say how you went about it and so you might add a sentence or phrase to indicate that and link into the methods section that follows.


The hypothesis investigated in this study was that supplementation of the diet with iron would result in improvements in cognitive function in pre-school children This was addressed through a randomised controlled trial.


And now work we need to work backwards from that statement. Where did the hypothesis or aims come from? Is there some doubt or controversy that the study aimed to clarify? Is this work just the next logical step in a chain of research? Where did that controversy or chain of research come from? These are all questions that you should be able to answer as you prepare your introduction. You won’t have done your research on a whim, or conjured a hypothesis from nowhere. None of us work in a vacuum and so your introduction has to succinctly pull together the strands of other research that led to your particular piece of work.


Moving still further back from your final statements, you will need to open the introduction with something fairly general, but topical and up-to-date about your subject area. This will be the hook on which you hang the whole paper. Think in terms of an opening that says X is an emerging problem; X has been of concern for some time and is increasing; X may represent a novel strategy for dealing with Y. All of these statements are just ways of saying that the general field in which you are adding just one small piece of new knowledge is really, really interesting or topical. Hopefully you believe that is the case, since you have invested your precious time in researching it.


Length and structure

I would suggest that you aim for no more than 500 words and you could probably write your introduction around 3 themes. As I generally work backwards these would be:


  • What were we trying to do (hypothesis and aims)?
  • What is the current dogma/cutting edge/ controversy that needs to be challenged or resolved?
  • Define the general area of research

Flip them around and you have your discussion- these could even be 3 paragraphs of 150 or so words each.

  • Define the general area of research
  • What is the current dogma/cutting edge/ controversy that needs to be challenged or resolved?
  • What were we trying to do (hypothesis and aims)?


An example

Let’s just look at this in a different way by analysing one of my recent introductory sections to a manuscript. This is the complete introduction and the first thing to note is that it is just 333 words long, so barely longer than the abstract. This reinforces the fact that the introduction is there just to set up the reason for the study, to justify why this paper is important. It wasn’t written to educate the reader, in fact quite the opposite. I generally assume that 90% of the people who read my papers have some expertise in the subject and that in fact they may only scan the introduction to see if there are any new references that they’ve not seen before and to find out what the aim of the study was.


The worldwide increase in the prevalence of overweight and obesity is increasingly impacting across all age-groups in the population (Ogden et al., 2013; WHO 2013). As a result all developed countries are reporting high levels of obesity among women of childbearing age and this has important consequences for maternal and fetal health during pregnancy, and potentially for the longer-term health of the children of obese women (Normia et al., 2013; Langley-Evans 2014; Taylor et al., 2014). In the UK 13 % of 21- to 30-year-old and 22 % of 31- to 40-year-old women were estimated to be obese in 2007, and this was expected to rise to 30 and 47 % respectively by 2050 (Foresight, 2007). 20% of UK women aged 16-44 were obese in 2010 (National Obesity Observatory, 2014) and in the USA (Ogden et al., 2013) this figure was approximately 32% in the 20-39 year old population. A dramatic increase in the prevalence of severe or morbid obesity has occurred alongside the increasing prevalence of obesity in young women and in 2009 approximately 5% of all pregnancies in England were associated with maternal BMI of over 35 kg/m2, with approximately 2% of pregnant women having BMI in excess of 40 kg/m2 (National Obesity Observatory 2014). Pregnancy is recognised as a period during which women are vulnerable to excessive weight gain that they may find difficult to reverse, thereby increasing risk for subsequent pregnancies and their longer-term health (Groth et al., 2013; Von Rueslen et al., 2014).


So, here we have the opening paragraph. This is defining the area of study. It is simply stating that obesity is increasing, is common in women of child-bearing age and that being pregnant is in itself a common risk factor for women to become obese. Notice that there are references in the section, but that they are all to recent papers. The introduction is not the place for an in-depth review or a history lesson in your field of interest. Short, sharp, focused and up-to-date should be your watchwords.


Maternal obesity during pregnancy increases the risk of adverse pregnancy outcomes, including miscarriage, gestational diabetes and hypertensive disorders (Sebire et al., 2001; Wang et al., 2002; Jensen et al., 2003; Maconochie et al., 2007; Centre for Maternal and Child Enquiries 2010; Li et al., 2013; Sommer et al., 2014). Obesity is recognised as a significant risk factor for maternal and fetal death (Centre for Maternal and Child Enquiries 2010). The risks associated with maternal overweight and excessive weight gain are recognised by the US Institute of Medicine (2009), which has published guidance on optimal ranges of weight gain during pregnancy. These are based upon maternal weight prior to pregnancy, with obese mothers advised to gain 5-9 kg across pregnancy, compared to the 12.5-18 kg recommendation for women of normal weight. The UK does not have any formal, evidence-based recommendations for healthy weight gain in pregnancy, although a guidance range of 10-12.5 kg is included within Department of Health literature. However, National Institute of Health and Clinical Excellence (NICE) guideline of 2010 recommends that health professionals carefully manage maternal weight. The emphasis of these guidelines is on weight loss prior to, or after pregnancy (NICE 2010). Weight loss is not advised during pregnancy as it may pose a risk to fetal nutrition and development.


So here I spell out one of the important challenges that exist in this field. We know that obesity is linked to poor pregnancy outcomes but at the moment we have no clearly defined strategy for managing the problem in obese mothers-to-be. Again, the review element here is light touch and references kept current. This is the section of the introduction where we should be presenting the current state-of-the-art, current balance of opinion (or lack thereof).


The antenatal period puts women into greater contact with health professionals and is therefore an ideal time for health education. Mothers are generally open and more readily motivated to make lifestyle changes that could benefit the health of themselves and their baby (Ritchie et al., 2010; Wilkinson & McIntyre 2012; Wilkinson et al. 2014; May et al., 2014). A number of studies have evaluated the impact of antenatal diet, exercise or weight management programmes upon pregnancy outcomes. Thornton and colleagues (2009) found that monitoring the food intake of obese women was associated with lower gestational weight gain and lower prevalence of gestational hypertension. Shirazian et al., (2010) reported that a lifestyle modification in obese pregnant women reduced weight gain, but had no effect on adverse pregnancy outcomes such as pre-eclampsia. The meta-analysis of Thangaratinam et al., (2012) found that weight management interventions in pregnancy reduced the risk of pre-eclampsia, but had no impact upon other obstetric outcomes. There are also a number of ongoing studies evaluating intervention strategies, such as the LIMIT trial in Australia (Dodd et al., 2011) and the UK UPBEAT study (Poston et al., 2013). Alongside randomised controlled trials of interventions, there are many clinical interventions mounted on a local level that aim to reduce the impact of maternal obesity upon health in the community. In this paper we report the findings of a service evaluation of one such programme. One-to-one antenatal guidance from midwives and healthy lifestyle advisors resulted in lower gestational weight gain and a reduced prevalence of gestational hypertension.


The last section of this introduction is perhaps not my finest hour now that I read it again, as the final sentences should be a snappier statement of aims or hypothesis. However, you can see it there in the highlighted section and it is followed with a sentence that is a taster of the paper outcomes (some journal editors really like this) which gives an indication of how the study was performed. The start of the paragraph flows from the second section. Having set up the challenge (the fact that there is no defined strategy) there is an offering of examples that show the findings of the literature are inconclusive in evaluating what happens when trying to meet that challenge.


A potted introduction, or introductory tool kit

So the introduction boils down to this fairly generic formula:


My area of research is of importance/interest because of this ______________________________. This is a new/old/well-established/emerging area.

The current state of knowledge in this area is ______________________________. Researchers in this field disagree on several key areas/agree that it is now essential to explore. We know a certain amount, such as ______________________, but _____________________ and ___________________ are still unanswered questions/unknowns/areas of controversy. 

As a result of an inconsistent literature/ following on from previous work in this field, we set out to address the hypothesis that/aim of ______________________________________. We did this by conducting an experiment/systematic review/qualitative study/survey/randomised controlled trial/etc.

Try writing one for yourself using this kind of structure. Delete the alternatives that don’t apply to you and fill in the blanks. This will probably give you a core of 150 words without even having to think too hard and you can flesh out the rest around that skeleton.


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