1. Paragraph Structure in Scientific Writing
Scientific Paper Writing Workshop
Quito, Ecuador
April 26–29, 2010
Suzanne Fischer, MS
Senior Editor
Family Health International
We’ll now talk briefly about ways to make your writing clear by paying attention to the structure of your paragraphs.

2. What is a paragraph?
“…A subject requires division into topics, each of which should be dealt with in a paragraph… The beginning of each paragraph is a signal that a new step in the development of the subject has been reached.”
Source: W. Strunk and E.B. White, The Elements of Style. 4th edition, 2000
So what is a paragraph? A paragraph is a collection of related sentences dealing with a single topic or sub-theme of a larger topic.
The Basic Rule: The basic rule of thumb with paragraphing is to keep one idea to one paragraph. If you begin to transition into a new idea, it belongs in a new paragraph.

3. Example of dividing topics by paragraphs
Several observations indicate that sand fly saliva is crucial in the establishment and pathogenesis of leishmaniasis. Saliva from sand flies markedly enhances the infectivity of Leishmania major in mice [4-6]. The mechanism by which the vector’s saliva enhances leishmania infection is not fully understood. Sand fly saliva contains potent antihemostatic and vasodilator compounds as well as potential immunomodulatory molecules that can directly down-modulate macrophage effector functions and facilitate the establishment of an infection [7,8].
I’ve extracted a part of the introduction section from a leishmaniasis paper to show how to divide topics into paragraphings. In this case, it would be fine to introduce a paragraph break after the second sentence, since the discussion of the mechanism is really a new thought, followed by supportive detail. Does that make sense?

4. Topic sentences
States the main idea of the paragraph in a single sentence
Generally, topic sentence is at beginning of a paragraph to ensure clarity
Each paragraph should have one central idea. The sentence that states the central idea of a paragraph is called a topic sentence. Everything else in the paragraph should support, illustrate, or otherwise closely relate to the topic sentence. We’ll look at some examples in a moment.

5. Supporting your topic sentence
Supporting facts or statistics
Examples
Comparisons
Cause and effect, reasons and consequences
Background information
Definitions
Adapted from: Susan Dakin, Paragraph structure, 2002
Once you have a topic sentence, the rest of the paragraph should be written in support of the topic. The topic should be discussed fully and adequately. This list provides examples of the kind of information that could be used in a paragraph to support your topic sentence.

6. Example: How is the topic sentence supported here?
Explaining technical terms and research concepts such as randomization and placebos to potential participants can be difficult. As a result, researchers have developed creative materials such as illustrated booklets, videos, and interactive computer-based educational programs to help explain them. Many trials also use a questionnaire to assess a woman's understanding of a study before she signs an informed consent form agreeing to participate in the study.
In this paragraph, the topic sentence explains a concept, and the following sentences describe some consequences.
Topic: explaining research concepts to participants can be difficult
Consequences: Researchers have developed materials to help them educate participants about research studies.

7. Example: How is the topic sentence supported here?
Populations of R. ecuadoriensis are widely distributed in Ecuadorian central and southern coastal regions, the southern Andean region of Ecuador, and northern Perú. In the coastal region, it is usually found in association with Phytelephas aequatorialis, an endemic palm species and squirrel and bird nests. In this region, there are frequent invasions and colonization by this species in the peridomestic and domestic habitats. However, R. ecuadoriensis is also frequently found in domestic and peridomestic habitats in El Oro province where palm trees are less abundant, and in Loja Province and Northern Perú, where palm trees are completely absent...
Here the topic sentence is supported by supporting facts and examples.

8. Example: How is the topic sentence supported here?
Excellent communication is the key to positive interactions with your adolescent clients. This means effectively sharing information as well as listening to the young people who come for counseling and testing. Use simple language and short sentences. Avoid technical terms. Ask open-ended questions and learn to read body language.
Here the topic sentence is supported by a definition of “excellent communication”.

9. Organizing structure Arrange ideas in clear order Chronological
Order of importance
General to specific
Specific to general
Question/answer or problem/solution
Now that you know the kinds of information that can support your topic sentence, let’s talk about how you can arrange your ideas in a clear order.

10. Chronological ordering
Searches of domicile and peridomicile were conducted by two-person teams using a modification of the one-man-hour method previously described. Briefly, if no bugs were found after the initial 20-min search, the searches were continued for an additional 10 min with the use of 6% pyrethrins solution that was hand sprayed in cracks and crevices as an irritant to prompt the exit of triatomines and increase collection efficiency. Collected triatomines were placed in individually labeled plastic containers and transported to either the field laboratory or the insectary.
A chronological ordering of ideas within a paragraph – such as this example, is often used in the methods section when describing the study processes you implemented.
(I edited this for brevity just to fit it on the slide.)

11. General to specific ordering
The risk factors for low birth weight (LBW), and their incidence, are important obstetric and general health indicators. Local surveillance and basic epidemiology are fundamental to assessing LBW and identifying areas to which future interventions should be targeted. The aims of the present study were to investigate the prevalence of and risk factors for LBW in western Sudan so as to add to our ongoing research on maternal and perinatal epidemiology in this setting, and on anaemia and its effects among pregnant Sudanese women.
In the results section of this paper, you can see in this example that the authors made good use of general to specific ordering.
Here the writer started with a broad idea—risk factors for low birth weight are important—and then narrowed it down to the very specific topic of the paper—risk factors for anemia and anemia’s effects on pregnant women in Sudan.

12. Checklist for paragraphs
Relevance
Coherence
Support for your topic
Emphasis
When you look over your papers again, check whether – on the paragraph level – you have written in a way that makes it easy for the reader to follow your study. The material given within each paragraph should pertain to or be relevant to the central idea, and you should provide adequate detail or comparisons or examples to develop each main point.
Relevance: Is every sentence relevant to the topic in the paragraph?
Coherence: Is there a logical and smooth flow of ideas?
Support for your topic: Do you provide detail, comparison, examples to develop each main point?
Emphasis: Is it clear to the reader which point is most significant within the paragraph?

13. Writing tip Use transitional words or phrases
“Since multiple malaria mosquito vectors are capable of transmitting both Plasmodium falciparum and P. vivax parasites, the two Plasmodium species co-exist in broad malaria-endemic regions. Therefore, an effective antimalarial vaccine for these regions would require components from both parasite species…” (Herrera, 2004)
Use transitional words or phrases such as “However,” or “In addition” or “For example” to lead your reader smoothly through the idea you are developing in any one/particular paragraph. There is a very nice color chart giving examples of transitional words – and when to use them – in your notebook under the tab marked “Paragraphs”.