How to Write the Introduction of a Quantitative Study: A Sentence-by-Sentence Breakdown

Writing a strong introduction is crucial to getting published, as it's the first section of your paper that journal reviewers read.

However, many authors are unsure of the best practices to follow when writing this section. How long should it be? Is my research purpose clear enough? Have I included enough context (or too much)?

Unfortunately, there are no one-size-fits-all responses to these questions, which makes writing an introduction even harder.

As a result, many authors end up writing introductions that contain several problems that make reviewers doubt the value of the study, such as:

• Lists of random background information

• Disorganized overviews of previous studies

• Research gaps that are not clearly related to the context

This happens because most authors don’t understand the main purpose of an introduction section. They think the introduction is there to provide background information and situate the current study within the literature.

Which is true, but most authors don't stop to think about why the introduction does these things. That is, they don't think about the real purpose of an introduction section:

The real purpose of the introduction is to present an argument for the existence of your study.

This article will show you how to make this argument.

Specifically, I will take a well-written introduction from a published study and break it down at the sentence level to show you how the authors made their study feel crucial to their field.

By the end of this article, you’ll see how a strong introduction section leaves readers feeling that the present study is not just interesting but vital.

Note: The advice in this article primarily relates to studies examining the relationship between a specific factor and one or more outcome variables (e.g., experimental studies, meta-analyses). While this article will still be of use to authors of other kinds of studies, not all the advice will be directly applicable to your paper.

Part One: Background

The introduction can be divided into two main parts. The first part, discussed presently, provides the background information.

However, this part of the introduction should do more than simply relay information about your topic and provide context for your study. According to an editorial published in the International Journal of Medical Education,

The purpose of providing background information in an introduction is to supply the context and other essential information concerning the research topic, and thus allow the reader to understand the significance of the specific research question and where it sits within the broader field of study.

In other words:

The goal of the first part of your introduction is to argue that your research topic is significant and, in turn, that your research question is worth answering.

This argument typically unfolds in three steps:

• The author proves that the broad research problem matters by identifying one or more significant negative outcomes.

• The author explains a specific cause of the problem mentioned in Step 1, or they present specific noteworthy outcomes of the problem.

• The author points out an unexplored component of a cause/outcome mentioned in Step 2 (which is the main variable examined in their study).

Step 1: Show that the broad research topic/problem is worth investigating.

To complete this step, first identify your research problem/topic. Then, clarify why the problem is worth resolving by providing evidence of its negative impacts on society.

This is often accomplished in a single sentence, as in this opening sentence from a meta-analysis published in Pediatrics (all subsequent examples used in this post are also taken from this study):

Example

Active maternal smoking during pregnancy is well recognized as a cause of fetal mortality and morbidity.

The authors have introduced the research topic (maternal smoking during pregnancy) and provided examples of its negative consequences (fetal mortality and fetal morbidity).

Step 2: Provide one or more causes or outcomes of the problem.

Once the research topic/problem has been identified, you’ll want to start gradually narrowing your focus toward your specific research objective or question.

This is done by naming specific causes or outcomes of the problem mentioned in Step 1.

Returning to our example, after explaining that maternal smoking during pregnancy causes fetal mortality and morbidity, the authors use the next few sentences to highlight several more specific outcomes of maternal smoking:

Example

These negative outcomes arise from being small for gestational age (10th centile for body weight corrected for gestation), low birth weight (2500 g), and premature birth (37 weeks’ gestation). Birth weights of infants of mothers who smoked during pregnancy are 250 g less than those born to nonsmoking mothers. Smoking during pregnancy has also been associated with increased risks of congenital malformations, particularly heart defects, limb-reduction defects, kidney/urinary tract defects, and cleft lip and palate defects.

Readers can now see that the present study deals with seven specific aspects of the broad problems of fetal mortality and morbidity, namely:

• being small for gestational age

• low birth weight

• premature birth

• heart defects

• limb-reduction defects

• kidney/urinary tract defects

• cleft lip and palate defects.

As it turns out, these seven consequences are the meta-analysis’s outcome variables.

With that in mind, we can already see the pieces of the argument locking into place: Because the study’s outcome variables are linked to fetal mortality and morbidity, they are worth studying.

Step 3: Identify unexplored alternate causes of the problem.

After identifying specific outcomes of the research problem in Step 2, you now want to turn the introduction section toward the specific factor(s) examined in your study.

This is typically done in one of two ways:

• Identifying a specific aspect of the problem mentioned in Step 1 that has not been fully explored.

• Noting other causes for the negative outcomes identified in Step 2 besides the problem mentioned in Step 1.

The authors of our example take the second route, mentioning secondhand smoking as an alternate cause of the outcomes listed in Step 2.

Example

Because secondhand smoke involves exposure to the same range of tobacco smoke toxins experienced by active smokers, although at lower levels, it is likely that exposure to secondhand smoke also causes some or all of these complications but with lower levels of relative risk. Therefore, secondhand smoke exposure to the mother during pregnancy may also have important effects on fetal health.

In addition to identifying an underexplored cause of fetal mortality and morbidity, this passage does two crucial things that shouldn't be overlooked:

• The authors provide their rationale for supposing that secondhand smoke has an effect. That is, they show that they have good reason to believe that secondhand smoke impacts the outcome variables named in Step 2.

• The authors shift from stating facts to making suggestions, as indicated by the use of words like "may" and "likely." This shift subtly lets readers know that the discussion is moving away from previous studies and toward the current study's objective.

Recap

By this point in the introduction, if we were to work backwards and reverse-engineer the argument, it would look something like this:

• The factor of interest identified in Step 3 is likely associated with the outcomes named in Step 2.

• The outcomes named in Step 2 are linked to a serious problem, as stated in Step 1.

• Therefore, the factor examined in this paper is worth studying.

From here, a strong introduction will go on to explain why the factor of interest needed to be studied in the way the authors chose to study it.

Part Two: Literature Gap

So, how do you argue that your specific study is necessary?

Like the first part of your argument, this part is also typically put forth in three steps:

• The author tells the reader what the literature says about the factor they investigated.

• The author highlights a gap in the literature.

• The author explains how the present study fills this gap and, therefore, was worth conducting.

Step 4: Explain what is known about the factor’s effect.

This part of the introduction shows what other researchers have already found about the currently examined factor.

This provides context to help readers see how the present study fits into the literature. It also provides the setup for the gap that will be mentioned in Step 5.

Example

After a recent systematic review and meta-analysis, we reported that secondhand smoke exposure in nonsmoking pregnant women decreases birth weight by 33 g and increases the risk of low birth weight (2500 g).

Here, the authors show that the factor they’ve examined has previously been found to influence one of the seven outcome variables noted earlier.

This leaves readers wondering, ‘What about the other outcome variables?’ which is precisely the question that the study aims to answer.

Step 5: Mention an unknown aspect of the factor’s effect.

This sentence builds off the previous one to highlight the research gap that your study addresses.

Example

However, the effect of maternal secondhand smoke exposure on other fetal outcomes, including mortality and congenital malformations, is less widely known.

Step 6: Explain how your study fills the knowledge gap.

The final piece of your argument is to show readers how your study contributes to filling the gap identified in Step 5.

In doing this, you will present your research objective, research questions, and/or hypotheses.

Example

Therefore, we report the results of a systematic review and meta-analysis of all the global evidence available to quantify the effect of maternal secondhand smoke exposure during pregnancy on a range of adverse fetal outcomes, including spontaneous abortion, fetal death, stillbirth, and major congenital malformations.

Here, the authors end their introduction by stating their research objective: "to quantify the effect of maternal secondhand smoke exposure during pregnancy on a range of adverse fetal outcomes."

They also very briefly mention what kind of study they conducted to achieve this objective ("a systematic review and meta-analysis").

Summary

At this point, you should now have a fully formed argument proving that your study was worth conducting (and is worth reading).

The exact form of the argument can vary, but, in general, it should look like this:

• The factor of interest identified in Step 3 is likely associated with the outcomes named in Step 2.

• The outcomes named in Step 2 are linked to a serious problem, as stated in Step 1.

• Therefore, the factor examined in this paper is worth studying.

• While some aspects of the factor’s effect are known (Step 4), no study has looked at the component highlighted in Step 5.

• The present study examines this underexplored component of the factor, as described in Step 6, thus filling a knowledge gap.

• Therefore, the present study will help resolve the vital problem posed in Step 1.

• Therefore, the study is both valuable and necessary.

To sum up this article in a sentence: No matter how much context you include, if readers don’t understand why your study needed to be conducted, then your introduction isn't doing its job.

This, in turn, drastically increases the chances that journal reviewers will reject your paper, even if it’s worth publishing.

Still unsure if your introduction section is strong enough?

I'd be happy to work with you one-on-one to ensure that every section of your paper clearly communicates the value of your paper. Click here to learn more.