Peer reviewers are in great demand in most areas of science. Requests to peer review manuscripts are a time-consuming, additional burden on already over-committed researchers (Hoppin 2002; Snell and Spencer 2005; Alberts et al. 2008; Kumar 2014). On the other hand, delays in the peer review process can be a frustrating bottleneck in the communication of new research findings (Bornmann and Daniel 2010; Cornelius 2012; Lyman 2013). Swift decisions might be regarded by authors as a sign of good organization and standing of a journal (Zhang et al. 2012; Lievers 2013). However, reviewers might tend to find the time to review manuscripts preferentially for journals that already have a good standing (Pautasso and Schäfer 2010). But how long does it take to deliver a peer review report for those researchers who do find the time? Available investigations are mainly based on data from medical journals, where a wide range of average peer review delays has been reported (Kljaković-Gašpić et al. 2003; Chen et al. 2013; Berquist 2014; Rosenkrantz and Harisinghani 2015). This editorial is based on data on about 7300 review reports delivered by 3001 reviewers for the European Journal of Plant Pathology (EJPP) over the last decade (2006–March 2015).

The average number of days needed to submit a peer review report was 29.2 (standard deviation = 19.1 days), the median was 27. This is very close to the deadline of 28 days suggested by the web-based manuscript handling system of the EJPP. However, there was important variation among reviewers, ranging from average delivery on the same day to taking 166 days (5 months and 10 days) (Fig. 1). About half of the reviewers needed up to 1 month on average (Fig. 2), with a further third of reviewers needing up to an additional 3 weeks on average to complete their report. There were about 7.5 % of reviewers needing more than 2 months. This long tail in the frequency distribution of the time needed to deliver a peer review report has also been documented for other journals (e.g. McPeek et al. 2009). These data do not include reviewers who were unassigned after agreeing to review a manuscript, because of late delivery.

Fig. 1
figure 1

Average number of days to complete a peer review report for the European Journal of Plant Pathology (2006–March 2015) by 3001 peer reviewers completing 7327 reports

Full size image
Fig. 2
figure 2

As in Fig. 1, but with the peer review time expressed in weeks rather than days

Full size image

About half of the reviewers registered in the EJPP peer reviewer database contributed one peer review report over the studied period, with a further 20 % of reviewers providing two reports, and another 20 % contributing three to five reports. However, there were 86 reviewers (3 %) who delivered at least 10 reports (maximum 32) over the 10 years studied. This 3 % of reviewers contributed about 17 % of the reports needed by the journal. Similarly, there were 379 reviewers (ca. 12 %) who delivered at least five reports. This 12 % of reviewers was responsible for about 40 % of reports. These assiduous reviewers are not necessarily prolific authors and conversely productive authors are not necessarily committed reviewers (Hochberg et al. 2009; Ghazoul 2011; Petchey et al. 2014).

The EJPP peer reviewer database also shows that for each completed peer review report, there is one peer review request which is either declined, not answered within 10 days, or not delivered after agreeing to do so. This obviously makes it more difficult and lengthy for handling editors to take a decision on a submitted manuscript (Bourne and Korngreen 2006; Hauser and Fehr 2007; Rohr and Martin 2012).

Overall, this database shows that it is possible for a good fraction of a scientific community to deliver timely review reports, but also that many researchers are not able to deliver on time, or to find the time do the job at all. An issue on which little information is available in the database is the quality of peer review reports (which can be graded, but is rarely assessed by editors), so that it is not possible to study whether there is a correlation between peer review delay and quality of the report (Paulus 2008; Hochberg 2015). Nevertheless, the time taken to deliver peer review reports should be included in metrics of peer reviewer contributions (Veríssimo and Roberts 2013; Cantor and Gero 2015).