The first IMRaD part of a scientific paper is the Introduction. The main purpose of the Introduction is to answer the following very simple question: ‘Why did you do this study?’ To answer that question, you need to briefly survey the literature, identify a gap in knowledge, and state your specific aim(s). In this note, I would like to offer you a strategy for writing the Introduction, and it is called “CaRS.”
Introduction: from general to specific
The Introduction of a scientific paper can be considered an educational material for readers. By reading the introduction, readers will have key concepts and ideas of the research project that the authors (you) are going to tell in the paper. Apart from learning about societal challenges, scientific issues, readers will learn scientific terminologies in the field. Thus, you can think of the Introduction as a way to educate your readers about your scientific concern and its significance.
The Introduction of a paper should be structured in the deductive format. When I said ‘deductive’, I mean the argument in the Introduction has to proceed from a general issue to a specific research question. In order words, the Introduction should begin with a big problem in the field, and end up with a specific research question or research aim.
A strategy for moving from general issue to specific issue is CaRS. CaRS stands for “Creating a Research Space.” The CaRS strategy is very popular among natural and social sciences writers. There are three steps in the strategy: first, you create a situation; second, you identify a niche for your study; and third, you occupy the niche. The ‘occupation’ of the nice means that you must state a research hypothesis (if possible) and then followed by a primary aim of the research project.
In the following, I am going to describe the CaRS strategy in more detail. I shall use two published papers on obesity (1) and rosiglitazone drug (2) to illustrate the writing strategy.
Tell readers: what are known
The first part of an introduction should be designed to create a situation. Here, you tell readers your research area, and the big issue that the field is currently facing. You also need to tell readers that the issue is of importance. And, there are several ways to demonstrate the importance, including the magnitude of the problem, the consequence of the problem in terms of human cost and societal impact. In short, the first part of an introduction is where you tell readers what is known.
For example, in a study of the relationship between obesity and body composition in Vietnam, the authors argue that obesity is an important global public health problem. They then characterize the importance in terms of high prevalence, morbidity consequences, and mortality. Here is their introduction (1):
“Obesity is recognized as a global health problem because it affects a large proportion of individuals in developed and developing countries. In the United States, 32% of adult men and 35% of adult women are obese (ie BMI ≥ 30 kg/m2). In Asia, approximately 17% of population is considered obese by World Health Organization (WHO). Obesity is associated with an increased risk of mortality, type 2 diabetes, cardiovascular diseases and cancer. Moreover, obese individuals have 7 times higher the risk of developing diabetes than individuals of a normal BMI. Since obesity is increased with advancing age, the on-going rapid aging of the population will further impose a greater burden on the society. Indeed, it has been estimated that by 2030 nearly one-third of the world population is overweight or obese.”
In a study of the adverse effects of rosiglitazone (a common anti-diabetic drug), the authors provide a brief but essential information concerning the use of thiazolidinedione. They write a nice very succinct introduction (2) as follows:
“Thiazolidinedione drugs are widely used to lower blood glucose levels in patients with type 2 diabetes mellitus. In the United States, three such agents have been introduced: troglitazone, which was removed from the market because of hepatotoxicity, and two currently available agents, rosiglitazone (Avandia, GlaxoSmithKline) and pioglitazone (Actos, Takeda). The thiazolidinediones are agonists for peroxisome-proliferator–activated receptor γ (PPAR-γ). PPAR-γ receptors are ligand-activated nuclear transcription factors that modulate gene expression, lowering blood glucose primarily by increasing insulin sensitivity in peripheral tissues. Rosiglitazone was introduced in 1999 and is widely used as monotherapy or in fixed-dose combinations with either metformin (Avandamet, GlaxoSmithKline) or glimepiride (Avandaryl, GlaxoSmithKline).”
Tell readers: what are unknown
The second part of an introduction should identify a nice, a gap in knowledge. The knowledge gap can be stated in terms of lack of data (or up-to-date data), a controversial viewpoint, or a novel method has not been applied. In short, here you tell readers what are unknown.
For the obesity study (1), the authors talk about the lack of consensus on the definition of obesity in Asian populations (1), and that can be considered a niche:
“Although it is believed that obesity is increasing in Asian populations, there is actually no consensus on the definition of obesity for Asians. In 2004, a WHO expert consultation concluded that Asian individuals are at greater risk of type 2 diabetes and cardiovascular disease with a lower BMI than their Caucasian counterparts, but the consultation did not come up with a consensus cut-off BMI for defining obesity in Asians. The consultation also proposed that the WHO BMI cut-off points should be retained as international classifications. In reality, some groups use the BMI ≥25 or BMI ≥27.5 as a cut-off value for the diagnosis of obesity in Asian men and women.”
For the rosiglitazone study, the authors identify the niche by pointing out that the drug was initially approved for its function of reducing blood glucose level, but its safety profile was not known. In addition, they point out that initial studies on potential adverse effects were based on small sample sizes, and therefore, could not detect a true association should it exist (2):
“The original approval of rosiglitazone was based on the ability of the drug to reduce blood glucose and glycated hemoglobin levels. Initial studies were not adequately powered to determine the effects of this agent on microvascular or macrovascular complications of diabetes, including cardiovascular morbidity and mortality. However, the effect of any antidiabetic therapy on cardiovascular outcomes is particularly important, because more than 65% of deaths in patients with diabetes are from cardiovascular causes.”
Tell readers: hypothesis and aim
Finally, the last paragraph of an introduction is where you occupy the niche that you have identified in the second part. “Occupation” here means that you propose a solution to the identified problem. The best way to state your solution is by stating a testable hypothesis and a specific research aim. Some people state more than 1 research aim, and that is fine too. I should mention that a hypothesis is a predictive statement, not simply a neutral statement.
In the obesity study (1), after pointing out that there has been lack of studies in the Vietnamese population, the authors state their research aim:
“Vietnam is a developing country with a population of approximately 92 million, representing 1.3% of the world population. Approximately 70% of the population lives in rural areas. During the past 20 years, the country has continued to be one of the world’s fastest economic growth, with annual growth rate of ~5%. Parallel with the economic development, Vietnam has also undergone remarkable changes in dietary patterns which led to a change in BMI. Therefore, the population is an ideal setting for studying the burden of obesity in transitional economies. However, no studies in the past have examined the burden of obesity using PBF as an indicator in Vietnam. Thus, in this study, we sought to analyze the association between PBF and BMI, and to define the prevalence of overweight and obesity using both BMI and PBF criteria.”
In the rosiglitazone study (2), having identified the lack of data concerning the potential adverse effects of the drug, the authors state their aim very clearly. They also make a preamble statement pertaining to the data that were used in the study:
“Therefore, we performed a meta-analysis of trials comparing rosiglitazone with placebo or active comparators to assess the effect of this agent on cardiovascular outcomes. The source material for this analysis consisted of publicly available data from the original registration package submitted to the Food and Drug Administration (FDA), another series of trials performed by the sponsor after approval, and two large, prospective, randomized trials designed to study additional indications for the drug.”
Although its structure is simple, it is not always straightforward to write a good introduction. In practice, I have seen many peer-reviewed papers that do not state any research aim or any hypothesis! Some common pitfalls I have seen are as follows:
· Exhaustive review of literature review. Some writers write a long introduction with so many historical information. That is probably not necessary because historical data can distract readers from the issue at hand. You don’t have to review the idea/issue from the time of Hippocrate; you simply get straight into the problem that you have identified.
· Failure to state the global problem behind your research. You should always start off with a big / global problem so that readers can have some idea which angle you are from.
· Failure to state the importance of the problem. Readers like to read papers that address an important problem, and it is your challenge to ‘hook’ them into your research world.
· Failure to state research aim. This is the worst pitfall in many many papers. It is annoying to read a 2-page introduction only to find out there is no specific aim! The lack of study aim or hypothesis is one of the common reasons for rejecting manuscripts.
In summary, the Introduction is an important component of a scientific paper, because it acts as an educational materials for readers. Based on the Introduction, readers will decide to continue reading the paper or not. The Introduction should ‘hook’ readers with 3-part structure: knowns, unknowns, and hypothesis/aim. The strategy for writing the Introduction is CaRS — creating a research space.
The introduction is sometimes likened to the gate of a scientific work. You, of course, want the gate to be attractive so that readers can enjoy your work. That means your introductory arguments should be clear, concise, analytic, and evidence-based. The clarity, precision and evidence will attract readers to explore other parts of the paper. To borrow the Greek motto, “a bad beginning makes a bad ending“, a bad introduction will likely make a bad conclusion.
Here is a check-list of the most important information that you should cover in the introduction:
• Have you answered the question: why did you undertake this study?
• Is there a specific aim or hypothesis?
• Is the research question important and impactful?
• Medical research paper: no more than 2 pages ?