I analyzed a random sample of 9,830 full-text research papers, uploaded to PubMed Central between the years 2016 and 2021, to answer the question:
How long should a paragraph be in a research paper?
I used the BioC API to download the data (see the References section below).
Paragraph length
Our sample of 9,830 research articles had 325,500 paragraphs. The following table summarizes the length of these paragraphs::
| Number of Sentences in a Paragraph | Number of Words in a Paragraph | |
|---|---|---|
| Minimum | 1 sentence | 1 word |
| 5th Percentile | 1 sentence | 19 words |
| 25th Percentile | 2 sentences | 65 words |
| 50th Percentile (Median) | 4 sentences | 109 words |
| Mean | 4.8 sentences | 125.2 words |
| 75th Percentile | 6 sentences | 167 words |
| 95th Percentile | 11 sentences | 286 words |
| Maximum | 61 sentences | 1,847 words |
From these data we can conclude that:
- The median paragraph length is 4 sentences (or 109 words), and most paragraphs are between 2 and 6 sentences (or 65 and 167 words).
- A paragraph can be just one sentence long. In fact, 13% (n=42,349) of all paragraphs in our sample were 1 sentence long.
- 90% of paragraphs were between 19 and 286 words (1 and 11 sentences). So, a paragraph shorter than 19 words can be considered too short; and a paragraph longer than 286 words (or 11 sentences) can be considered too long.
Paragraph length in each section of the research paper
A research paper is usually divided into 4 sections: Introduction, Methods, Results, and Discussion. The following table shows the median paragraph length for each of these sections:
| Median Paragraph Length | ||
|---|---|---|
| Research Paper Section | Sentence Count | Word Count |
| Introduction | 4 sentences | 113 words |
| Methods | 4 sentences | 92 words |
| Results | 4 sentences | 105 words |
| Discussion | 5 sentences | 131 words |
The Discussion section has slightly longer paragraphs than other sections with a median of 5 sentences and 131 words.
Paragraph length in different types of studies
The data suggests that paragraph length did not differ for different study designs. Review papers (systematic reviews and meta-analyses) had almost the same paragraph length (median=103 words) as original research papers (median=110 words).
References
- Comeau DC, Wei CH, Islamaj Doğan R, and Lu Z. PMC text mining subset in BioC: about 3 million full text articles and growing, Bioinformatics, btz070, 2019.