As the number of scientific papers published every year continues to grow, individual papers are also becoming increasingly specialised and complex (Delanty, 1998; Bornmann and Mutz, 2015; Doubleday and Connell, 2017; Cordero et al., 2016; Plavén-Sigray et al., 2017). This information overload is driving a ‘knowledge-ignorance paradox’ whereby information increases but knowledge that can be put to good use does not (Jeschke et al., 2019). Writing scientific papers that are clearer to read could help to close this gap and increase the usefulness of scientific research (Freeling et al., 2019; Letchford et al., 2015; Heard, 2014; Glasziou et al., 2014).
One feature that can make scientific papers difficult to read is the widespread use of acronyms (Sword, 2012; Pinker, 2015; Hales et al., 2017; Lowe, 2019), and many researchers have given examples of the overuse of acronyms, and highlighted the ambiguities, misunderstandings and inefficiencies they cause (Fred and Cheng, 2003; Narod et al., 2016; Patel and Rashid, 2009; Pottegård et al., 2014; Weale et al., 2018; Parvaiz et al., 2006; Chang et al., 2002). For example, the acronym UA has 18 different meanings in medicine (Lang, 2019).
In this article we report trends in the use of acronyms in the scientific literature from 1950 to the present. We examined acronyms because they can be objectively identified and reflect changes in specialisation and clarity in writing.
We analysed 24,873,372 titles and 18,249,091 abstracts published between 1950 and 2019, which yielded 1,112,345 unique acronyms. We defined an acronym as a word in which half or more of the characters are upper case letters. For example, mRNA and BRCA1 are both acronyms according to this definition, but N95 is not because two of the three characters are not upper case letters.
We found that the proportion of acronyms in titles increased from 0.7 per 100 words in 1950 to 2.4 per 100 words in 2019 (Figure 1); the proportion of acronyms in abstracts also increased, from 0.4 per 100 words in 1956 to 4.1 per 100 words in 2019. There was at least one acronym in 19% of titles and 73% of abstracts. Three letter acronyms (jokingly called TLAs) were also more popular than acronyms of two and four letters.
The proportion of acronyms in titles has flattened since around the year 2000, whereas the proportion in abstracts continued to increase. Moreover, when the 100 most popular acronyms were removed, there was still a clear increase in acronym use over time (Figure 1—figure supplement 1). Furthermore, the increase was visible in all the article types we studied (including articles, clinical trials, case reports, comments and editorials: Figure 1—figure supplement 2; Figure 1—figure supplement 3). Video 1 shows the top ten acronyms in titles for every year from 1950 to 2019, and Video 2 shows the top ten acronyms in abstracts over the same period.
Video 1: The top ten acronyms in titles for every year from 1950 to 2019.
Video 2: The top ten acronyms in abstracts for every year from 1950 to 2019.
There are 17,576 possible three-letter acronyms using the upper case letters of the alphabet. We found that 94% of these combinations had been used at least once. Strikingly, out of the 1.1 million acronyms analysed, we found that the majority were rarely used, with 30% occurring only once, and 49% occurring between two and ten time times. Only 0.2% of acronyms (just over 2,000) occurred more than 10,000 times.
One year after their first use, only 11% of acronyms had been re-used in a different paper in the same journal. Longer acronyms were less likely to be re-used, with a 17% re-use for two-character acronyms, compared with just 8% for acronyms of five characters or longer. The time taken for acronyms to be re-used has also increased over time (Figure 2), indicating that acronyms created today are less likely to be re-used than previously created acronyms.
DNA is by far the most common acronym and is universally recognised by scientists and the public (Table 1). However, not all the top 20 may be so widely recognised, and it is an interesting individual exercise to test whether you, the reader, recognise them all. Six of the top 20 acronyms also have multiple common meanings in the health and medical literature, such as US and HR‚ although the meaning can usually be inferred from the sentence.
In parallel with increasing acronym use, the average number of words in titles and abstracts has increased over time, with a steady and predominantly linear increase for titles, and a more nonlinear increase for abstracts (Figure 3). The average title length increased from 9.0 words in 1950 to 14.6 words in 2019, and shows no sign of flattening. The average abstract length has also increased, from 128 words in 1962 to 220 words in 2019, and again this trend shows no sign of flattening. It is worth pointing out that these increases have happened despite the word and character limits that many journals place on the length of titles and abstracts.
Our results show a clear increase over time in the use of acronyms titles and abstracts (Figure 1), with most acronyms being used less than 10 times. Titles and abstracts are also getting longer (Figure 3), meaning readers are now required to read more content of greater complexity.
There have been many calls to reduce the use of acronyms and jargon in scientific papers (see, for example, Talk Medicine BMJ, 2019, which recommends a maximum of three acronyms per paper), and many journal and academic writing guides recommend a sparing use of acronyms (Sword, 2012). However, the trends we report suggest that many scientists either ignore these guidelines or simply emulate what has come before. Entrenched writing styles in science are difficult to shift (Doubleday and Connell, 2017), and the creation of new acronyms has become an acceptable part of scientific practice, and for clinical trials is a recognised form of branding (Pottegård et al., 2014).
We believe that scientists should use fewer acronyms when writing scientific papers. In particular, they should avoid using acronyms that might save a small amount of ink but do not save any syllables, such as writing HR instead of heart rate (Pinker, 2015; Lang, 2019). This approach might also make articles easier to read and understand, and even help avoid potential confusion (as HR can also mean hazard ratio or hour). For more complex phrases with multiple syllables and specialist words, such as methylcyclopentadienyl manganese tricarbonyl (MMT), acronyms may ease reading and aid understanding, although MMT might mean methadone maintenance treatment to some readers.
It is difficult to make a general rule about which acronyms to keep and which to spell out. However, there is scope for journals to reduce the use of acronyms by, for example, only permitting the use of certain established acronyms (although the list of allowed acronyms would have to vary from journal to journal). In the future it might be possible, software permitting, for journals to offer two versions of the same paper, one with acronyms and without, so that the reader can select the version they prefer.
Our work shows that new acronyms are too common, and common acronyms are too rare. Reducing acronyms should boost understanding and reduce the gap between the information we produce and the knowledge that we use (Jeschke et al., 2019)‚ without ‘dumbing down’ the science. We suggest a second use for DNA: do not abbreviate.
Adrian Barnett is with the School of Public Health and Social Work, Queensland University of Technology, Australia. Zoe Doubleday is with the Future Industries Institute, University of South Australia, Australia.