What's the evidence for outline numbering?

November 2017


Earnsy Liu, TechCommNZ member and GDID student, looks for evidence (not just opinions) to help you manage the daily conundrums we face in our profession. If you have a question for Earnsy to tackle, please email comms@techcomm.nz. In this post, Earnsy looks deeper into the debate around outline numbering.

The jury is out on outline numbering

Who would’ve thought that outline numbering could make for lively debate? I certainly didn’t, but it turns out that lots of people have a view on it. The person who suggested this topic did. Her exact words need to be censored but trust me, she wasn’t a supporter!

What’s outline numbering? I took it to mean a numbered hierarchy of headings and possibly paragraphs. ‘Numbering’ could also use letters or roman numerals. Here’s an example from the Health and Safety at Work Act (2015):

The section uses alphanumeric numbering with Arabic numerals, a letter, and roman numerals. The screenshot shows 17.1.a.i

Figure 1: An example of numbering in health and safety legislation.

Numbering is used in legislation, council bylaws, reference documents, and some journal articles. Oh, and in the TechCommNZ constitution.

Is it good or bad? Let’s look at research, technical communicators’ opinions, and expert advice.

Not much research

There are theories and models, such as how headings ‘may communicate [hierarchical] information… with lettering and/or numbering of text sections’ (Lemarié, Lorch, & Péry-Woodley, 2012, p. 12). But there doesn’t seem to be any recent research specifically about numbering.

Klusewitz and Lorch (2000) examined four types of headings in a text-search study, including structure (numbered) and topic (plain) headings (see figure 2). The experiment, which used print notebooks, showed little evidence that headings or cues on hierarchy affected search strategies.

It’s best not to read too much into these findings, though. The researchers weren’t examining numbering per se, but headings generally, and the researchers admit the search task was ‘very rudimentary’ (p. 675). Plus, numbering wasn’t the only difference between the two conditions; indentation was different too.

Numbered headings Plain headings

The first level heading is numbered 1 and centred. The second level heading is numbered capital A and left aligned. The third level heading is numbered 1 and indented. All levels are capitalised.

None of the headings are numbered or indented. However, all are capitalised.

Figure 2: The numbered headings used indentation to indicate hierarchy. In contrast, not only were the plain headings not numbered, their left-alignment meant they lacked hierarchical cues (Klusewitz & Lorch, 2000, p. 668).

Opinions aplenty

Numbering has been discussed several times on the TechWhirl forum, with at least two dozen users chiming in on two occasions. Although that was in 1996 and 2001, when formatting was more basic and we used print more than screens, some opinions still apply. For one thing, ‘real users’ still print, as Meredith Evans reminded us at this year’s conference.

See what you think of the arguments for and against numbering, and read an expert’s current opinion.

For numbering

Navigation and orientation

  • Cross-referencing is easier ‘than saying 3 paragraphs previous’ (Wiley, cited in Anthony, 1996).
  • It orientates readers. ‘Usually the headings don't differ that much in size or style that I could tell at once which heading level that is’ (Reng, cited in Joseph, 2001b). And numbering long, complex documents ‘[gives] an indication of where you are in the section and where you are in the document’ (Posada, cited in Joseph, 2001b).
  • Navigating is easier. ‘When I jump from one topic to another and want to go back I have more problems to find the previous heading when I don't have numbers’. Similarly when navigating from a table of contents (Reng, cited in Joseph, 2001b).
  • Non-native speakers find it easier because ‘numbered headings give them an additional "road sign"’ (Beilby, cited in Joseph, 2001b).

Reader preference

  • ‘Technical’ readers like it: ‘Many technical people are used to this format and really prefer it … because it's easier to refer to the sections in the document.’ (Beilby, cited in Joseph, 2001b)

    ‘By training/education (PhD Chemistry) and experience I'm a technical person. Most of the documents I come across have section numbers. I use them extensively myself. Us [sic] techies tend to like numbers!’ (Robertson, cited in Anthony, 1996)

    (This ‘technical’ preference seems real. Woolever (2008), author of Writing for the Technical Professions , discusses numbering for ‘technical reports, especially engineering reports’ (p. 303). Curious, I looked up two engineering documents. True enough, both were numbered.)

  • Some readers are accustomed to it ‘where the numbering scheme is so well-defined and universal for a specific subject that everyone has long since memorized the numbering scheme’ (Hart, cited in Joseph, 2001a).

Document structure

  • Writers organise better. ‘In general, it's much harder to write documentation whose structure is completely self-explanatory without some help from a multi-level numbering scheme.’ Formal numbering ‘imposes a discipline on the writer to organize the material in a logical way’ and makes editing easier (White, cited in Anthony, 1996).

    (Purdue Online Writing Lab (2010) mentions this organisational benefit too.)

  • Documents are consistent. ’Numbered headings work best with parallel structured documents that spans [sic] an entire document set. If section 5 covers the same content in every book, and section .3 is the same aspect, then numbered headings will work’ (Locke, cited in Joseph, 2001a).
  • References are unique. Numbering means you don’t end up with identical headings if a subject is discussed in different chapters (Rands, cited in Joseph, 2001b).

Against numbering

Reader preference

  • Users don’t like it: Some users find visual cues more helpful (Bronson, cited in Joseph, 2001a). Also, ‘non-technical users can be intimidated by section numbers’ (Gallagher, cited in Anthony, 1996).

Not helpful

  • They distract. ‘If you can cross-refer to headings and pages, section numbers are not just superfluous, they actually make the heading harder to understand and memorise. The number is clutter containing no useful information’ (Sunders, cited in Joseph, 2001a). ‘The eye can't find the heading text because it jumps to the number’ (Neuburger, cited in Anthony, 1996).
  • Headings and page numbers are more useful : ‘Referring to a heading is complicated because if it is a physical (printed) document, you need the page number more that [sic] the heading numbering. Once on the page the text description (heading text) is more recognizable that [sic] numbers’ (Scott, cited in Joseph, 2001a).
  • It’s no longer necessary: We can now create cross-references to headings and page numbers (Hart, cited in Joseph, 2001a). Section numbers were useful when ‘we were using courier 10 and only had bold and underline’ and had limited visual tools for differentiating levels (Hamilton, cited in Anthony, 1996).

An expert’s opinion

Plain language specialist Redish agrees that ‘finding the right part is easier by number than by name’, for example in contracts. ‘Numbering is also traditional — and traditionally useful — in laws, regulations, and other legal documents that have many cross-references.

However, that tradition (and usefulness) is print-based. If everyone is going to read and use the document online where references and cross-references can be links, words are often better than numbers because they carry more meaning. But I suspect that lawyers who write laws and regulations would argue that the names would often be very long and cumbersome’ (personal communication, August 22, 2017).

Expert advice

We don’t have to use numbered outlines, but they ‘help readers to navigate through [a] report, and, if necessary, comment on it more easily’ (Cutts, 2009, pp. 142-143).

This is especially the case for ‘complex works, such as textbooks and practitioner texts’ or ‘large reports’ (“Paragraphs,” 2012, p. 16; Woolever, 2008, p. 303).

Numbering systems

The Plain English Campaign suggests numbering isn’t necessary with clear headings and a detailed table of contents. But if it is, ‘use capital letters to label sections and numbers to label paragraphs (A1, A2 and so on)’ (2001, p. 19).

Other authorities suggest either alphanumeric or decimal numbering.

  • Purdue OWL (n.d.) considers the following system (the same one for American legal documents) ‘the most common type of outline and usually instantly recognizable to most people’:

Roman numerals
Capitalized letters
Arabic numerals
Lowercase letters

A, B, C
1, 2, 3
a, b, c

  • But it also promotes the decimal system (for example, 1.2.2), which shows the relationship between parts.
  • Reep (2009), a professor of English, is fine with either system, depending on preference and company style.

Yet others prefer a numeric system:

  • The New Oxford Style Manual recommends and uses a decimal system (“Paragraphs,” 2012).
  • Cutts (2009), a plain English champion, suggests a decimal system.
  • US lawyer and typographer Butterick (n.d.) advocates a decimal system over the traditional alphanumeric system, which he calls ‘a terrible way to label hierarchical headings’. He laments: ‘Roman numerals and romanettes stink’, ‘Letters aren’t much better’, and ‘Mixing roman numerals and letters results in ambiguous references’). His short, delightful argument is worth reading.
  • The Web Content Accessibility Guidelines likewise recommend a decimal system over simple numbers, because it provides more context (W3C, 2000).

Arabic or Roman numerals

How quickly and confidently can you read the numbers below?

Side view showing the numbers X, VI, IV, VIII, and II.

Figure 3: Roman numerals on die (image by Wintermute115; CC licence 4.0)

If you hesitated, you’re in good company. People take longer and made more mistakes when reading Roman numerals, especially when numbers are large (Perry, cited in Doherty, 2015; see figure 4). Although this was a 1952 study, the findings probably still apply. What’s XII and XCIX, by the way?

Differences in comprehension speed and errors increase with number size.

Figure 4: Participants read Arabic numerals faster and more accurately than Roman numerals, especially when numbers were large. (Adapted from Perry, cited in Doherty 2015.)

There’s another reason to opt for Arabic numerals: accessibility. The British Dyslexia Association’s style guide discourages Roman numerals (n.d., p. 3). Kevin Prince suspects people with dyslexia are likely to confuse Arabic numerals with letters in words. His quick check showed a screen reader read the numeral ‘i' as ‘aye’, which is also confusing. But generally, he thinks ‘outline numbering is more likely to help than hinder, particularly where you have the kind of document where you need to reference clearly’ (personal communication, August 17, 2017).

How many levels to number

Cutts (2009) suggests numbering one level: ’If you use a second tier of heading, you don’t need to number it but you should distinguish it by layout’. Or maybe two levels: ‘Avoid creating a third or fourth level of decimals (3.1.2 etc.) unless the amount of detail really demands it.’ (pp. 142-143)

The New Oxford Style Manual suggests three levels, as does Woolever, who explains that otherwise ‘the table of contents (which must include all of the numbers) will resemble a data stream and be harder to read, not easier.’ If you want more levels in the text, she suggests limiting it to three in the table of contents. (p. 304).

Paragraph numbering

Should we number paragraphs? Expert advice is mixed. In order of enthusiasm:

  • It’s OK with Cutts: ‘An alternative to a decimal system is simply to number paragraphs in 1-2-3 order’ (2009, p. 143).
  • It’s OK with the New Oxford Style Manual for ‘complex works, such as textbooks and practitioner texts’ or ‘when an author wishes to enumerate long points in an argument’ (“Paragraphs,” 2012, p. 16).
  • If it’s necessary, ‘keep it as simple as possible’ (Plain English Campaign, 2001, p. 19).
  • Don’t. ‘Don’t get so carried away with numbering that you number each paragraph. Doing so causes the decimals to string out so far that they overwhelm the text on the page: “ Technical Developments”’ (Woolever, 2008, p. 304).

I liked how one lawyer put it: ‘If you don’t have to use a numbered-paragraph format, don’t. When you do have to … treat the numbers as just a little detail that you are required to add in front of each of your paragraphs. Write as if they aren’t there, with headers, subheaders, transitional sentences, and all of your normal tools of organization’ (Griffis, 2013). That’s exactly what the journal Discours does:

Paragraph number appears in small grey font to the left of the text.

Figure 5: Unobtrusive numbers in the journal Discours allow paragraphs to be referenced easily.

How now?

So we have precious little research, lots of opinions, and some expert advice to use numbered headings if suitable.

How do we decide? A TechWhirl contributor suggested: ‘To get rid of section numbering, do a usability study and ask readers if they refer to sections that way’ (Locke, cited in Anthony, 1996). I’d add: find out if they read on paper or on screen.

If you use numbering, consider a simple decimal system and keep to no more than three levels.


My thanks to Ginny Redish for her thoughts on this topic, and Paul Doherty for kindly sharing his article.


Anthony, M. (1996, Sep 11). Summary: Pros/cons of section numbering [Online forum comment]. Retrieved from http://www.techwr-l.com/archives/9609/techwhirl-9609-00488.html

British Dyslexia Association. (n.d.). Dyslexia style guide. Retrieved from the British Dyslexia Association website: www.bdadyslexia.org.uk/common/ckeditor/filemanager/userfiles/About_Us/policies/Dyslexia_Style_Guide.pdf

Butterick, M. (n.d.). Hierarchical headings. Retrieved from Typography for Lawyers website: http://typographyforlawyers.com/hierarchical-headings.html

Cutts, M. (2009). Oxford guide to plain English (3rd ed.). New York, NY: Oxford University Press.

Doherty, P. E. (2015). A study of the effects of spatial contiguity and hierarchically structured headings in a shipboard operating and maintenance manual. WMU Journal of Maritime Affairs, 15(1), 97-125.

Griffis, K. (2013, June 4). Numbered paragraphs. Retrieved from Brief Right website: http://briefright.com/numbered-paragraphs/

Joseph, B. (2001, Sep 21a). Summary part 1– Numbered headings [Online forum comment]. Retrieved from http://www.techwr-l.com/archives/0109/techwhirl-0109-01108.html

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Lemarié, J., Lorch, J. R. F., & Péry-Woodley, M. P. (2012). Understanding how headings influence text processing. Discours. Revue de linguistique, psycholinguistique et informatique. A Journal of Linguistics, Psycholinguistics and Computational Linguistics , (10). Retrieved from http://discours.revues.org/8600

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Plain English Campaign. (2001). How to write reports in plain English. Retrieved from http://www.plainenglish.co.uk/files/reportsguide.pdf

Purdue OWL. (2010). Why and how to create a useful outline . Retrieved from Purdue Online Writing Lab website: https://owl.english.purdue.edu/owl/resource/544/02/

Purdue OWL. (n.d.). Types of outlines and samples. Retrieved from Purdue Online Writing Lab website: https://owl.english.purdue.edu/owl/resource/544/03/

Reep, D. (2009). Finding out about readers. In Technical writing: Principles, strategies, and readings (7 th ed.) New York, NY: Pearson Education.

W3C. (2000). HTML Techniques for Web Content Accessibility Guidelines 1.0 . Retrieved from W3C website: https://www.w3.org/TR/WCAG10-HTML-TECHS/

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