I analyzed a random sample of 61,514 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 methods 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 methods section was 1,126 words long (equivalent to 45 sentences, or 10 paragraphs), and 90% of the methods sections were between 372 and 2,674 words.
2. Compared to other sections in a research paper, the methods was about the same length as either the results or the discussion, and double the length of the introduction.
3. Review articles have the shortest methods sections overall, and experimental and quasi-experimental design articles have the longest methods sections.
4. In general, articles published in higher impact journals include a more detailed description of the materials and methods used.
Overall length of the methods section
Here’s a table that describes the length of a methods section in terms of words, sentences, and paragraphs:
|Methods Section Length|
|Word Count||Sentence Count||Paragraph Count|
|Minimum||7 words||1 sentence||1 paragraph|
|25th Percentile||757 words||31 sentences||6 paragraphs|
|50th Percentile (Median)||1,126 words||45 sentences||10 paragraphs|
|Mean||1,278.8 words||50.8 sentences||11.1 paragraphs|
|75th Percentile||1,620 words||64 sentences||14 paragraphs|
|Maximum||18,517 words||931 sentences||336 paragraphs|
From these data, we can conclude that the methods sections in most research papers are between 6 and 14 paragraphs (31 to 64 sentences).
The methods section constitutes 29.7% of the total word count in a research article, equivalent to the length of either the results or the discussion, and double that of the introduction [source: How Long Should a Research Paper Be?].
Length of the methods for different article types
The following table shows the median word count of the methods section for different study designs:
|Study design||Number of studies in the sample||Median methods word count|
|Case series||140 studies||567 words|
|Systematic review||689 studies||760 words|
|Meta-analysis||1,481 studies||849 words|
|Case-control||443 studies||931 words|
|Cross-sectional||3,529 studies||963 words|
|Case-report||407 studies||1,032 words|
|Cohort||5,181 studies||1,092 words|
|Pilot study||686 studies||1,140 words|
|Quasi-experiment||144 studies||1,177 words|
|Randomized controlled trial||842 studies||1,217 words|
The data show that, in general, review articles (systematic reviews and meta-analyses) have shorter methods sections than average, and experimental and quasi-experimental designs require more detailed methods sections than average.
Length of the methods in different journals
In order to study the influence of the journal quality on the length of the methods section, I ran a Poisson regression that models the methods word count given the journal impact factor. Here’s the model output:
|Journal impact factor||0.049||<0.001||<0.001|
The model shows that a higher journal impact factor is associated with a longer methods section. Specifically, a 1 unit increase in the journal impact factor is associated with an increase of 5% in the methods word count. For the median article, this means that a 1 unit increase in the journal impact factor is associated with an increase in 56 words in the methods section.
So the data suggest that, in general, articles published in higher impact journals include a more detailed description of the materials and methods used.
- 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.
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