In the introduction, you are attempting to inform the reader about the rationale behind the work, justifying why your work is an essential component of research in the field.
The introduction does not have a strict word limit, unlike the abstract, but it should be as concise as possible. It can be a tricky part of the paper to write, so many scientists and researchers prefer to write it last, ensuring that they miss no major points.
The introduction gives an overall review of the paper, but does address a few slightly different issues from the abstract.
It works upon the principle of introducing the topic of the paper and setting it into a broad context, gradually narrowing down to a research problem, thesis and hypothesis. A good introduction explains how you mean to solve the research problem, and creates ‘leads’ to make the reader want to delve further into your work.
You should assume that your paper is aimed at someone with a good working knowledge of your particular field.
For example, a paper about evolutionary adaptations need not go into too much detail about Darwin - it is fairly common knowledge.
A behavioral science paper only needs to mention Pavlov and Skinner in passing, as their theories are standard for any first year undergraduate.
Like in any good Hollywood movie, the first task of the introduction is to set the scene, giving your paper a context and seeing how it fits in with previous research in the field.
Whilst not the only way, this section, comprising the first paragraphs of your introduction, can be based around a historical narrative, from the very first research in the field to the current day.
In many fields, this could make up an entire essay in itself, so you have to stick to relevant information.
This leads into the rationale behind the research, revealing whether it is building upon previous research, looking at something that everybody else has overlooked, or improving upon a previous research project that delivered unclear results.
This section can then flow into how you are going to fill the gap, laying out your objectives and methodology. You are trying to predict what impact your research will have if everything works as it should, and you ultimately reject the null hypothesis.
The introduction is the place to highlight any weaknesses in the experiment from the start.
For example, an ideal experiment should have perfectly randomized samples, but there are many good reasons why this is not always possible. As long as you warn the reader about this, so that they are aware of the shortcomings, then they can easily judge the validity of the research.
This is much better than making them wait until you point it out in the discussion.
You should also point out any assumptions that you make about conditions during the research. You should set out your basic principles before embarking upon the experiment: any research will be built around some assumptions.
For example, if you were performing educational research, you may assume that all students at the same school are from a very similar socio-economic background, with randomization smoothing out any variables.
There are a few tips that can help you write a strong introduction, arousing interest and encouraging the reader to read the rest of your work.
Keep it Short A long and rambling introduction will soon put people off and lose you marks. Stick closely to your outline for the paper, and structure your introduction in a similar way.
Define the Problem The entire introduction should logically end at the research question and thesis statement or hypothesis. The reader, by the end of the introduction, should know exactly what you are trying to achieve with the paper. In addition, your conclusion and discussion will refer back to the introduction, and this is easier if you have a clearly defined problem.
Organization As you write the paper, you may find that it goes in a slightly different direction than planned. In this case, go with the flow, but make sure that you adjust the introduction accordingly. Some people work entirely from an outline and then write the introduction as the last part of the process. This is fine if it works for you.
Once your introduction is complete, you can now think about attacking the rest of the paper.