I analyzed a random sample of 61,517 full-text research papers, uploaded to PubMed Central between the years 2016 and 2021, in order to answer the questions:
What is the typical length of a discussion section? and which factors influence it?
I used the BioC API to download the data (see the References section below).
Here’s a summary of the key findings
1. The median discussion section was 1,115 words long (equivalent to 43 sentences, or 7 paragraphs), and 90% of the discussion sections were between 482 and 2,230 words.
2. Compared to other sections in a research paper, the discussion was about the same length as either the methods or the results, and double the length of the introduction.
3. The length of the discussion does not differ between review articles and original research articles.
4. The quality of the journal does not influence the length of the discussion section.
Overall length of the discussion section
Here’s a table that describes the length of a discussion section in terms of words, sentences, and paragraphs:
| Discussion Section Length | |||
|---|---|---|---|
| Word Count | Sentence Count | Paragraph Count | |
| Minimum | 40 words | 1 sentence | 1 paragraph |
| 25th Percentile | 824 words | 32 sentences | 5 paragraphs |
| 50th Percentile (Median) | 1,115 words | 43 sentences | 7 paragraphs |
| Mean | 1,206.8 words | 46.4 sentences | 7.8 paragraphs |
| 75th Percentile | 1,480 words | 57 sentences | 9 paragraphs |
| Maximum | 32,816 words | 2,006 sentences | 981 paragraphs |
From these data, we can conclude that the discussion sections in most research papers are between 824 and 1,480 words long (32 to 57 sentences).
If you are interested, here are the links to the articles with the shortest and longest discussion sections.
The discussion section constitutes 29.5% of the total word count in a research article, equivalent to the length of either the methods or the results, and double the length of the introduction [source: How Long Should a Research Paper Be?].
Length of the discussion for different article types
The following table shows the median word count of the discussion section for different study designs:
| Study design | Number of studies in the sample | Median discussion word count |
|---|---|---|
| Case series | 140 studies | 1,003 words |
| Case-control | 443 studies | 1,016 words |
| Randomized controlled trial | 842 studies | 1,066 words |
| Case report | 407 studies | 1,077 words |
| Meta-analysis | 1,481 studies | 1,116 words |
| Quasi-experiment | 144 studies | 1,117 words |
| Cross-sectional | 3,529 studies | 1,128 words |
| Cohort | 5,180 studies | 1,164 words |
| Pilot study | 686 studies | 1,185 words |
| Systematic review | 689 studies | 1,210 words |
The data show no clear pattern since the discussions of review articles and original research articles have almost similar word counts. So we can conclude that there is no particular article type that requires a longer discussion section.
Length of the discussion in different journals
In order to study the influence of the journal quality on the length of the discussion section, I ran a Poisson regression that models the discussion word count given the journal impact factor. Here’s the model output:
| Variables | Coefficient | Standard error | p-value |
|---|---|---|---|
| (Intercept) | 7.114 | <0.001 | <0.001 |
| Journal impact factor | 0.001 | <0.001 | <0.001 |
The model shows that a higher journal impact factor is associated with a slightly longer discussion section. Although statistically significant, this effect is practically negligible since a 1 unit increase in the journal impact factor is associated with an increase of only 0.1% in the discussion word count. For the median article, this means that a 1 unit increase in the journal impact factor is associated with an approximate increase of 1 word in the discussion section.
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.