The authors of the paper published in Research Integrity and Peer Review found that, in 2020, reviewers worldwide spent over 100 million hours on peer reviews—equivalent to more than 15,000 years of labor. The estimated monetary value of the time contributed by reviewers in the US, China, and the UK alone exceeded $2 billion.
Also worth examining is a ranking of 28 European countries based on the ratio of reviewers with more than 400 confirmed peer reviews (from journals indexed in Web of Science) per million inhabitants. The data reveals that researchers in Germany and France are among the least inclined to donate their time. At the top of the list, however, is my own country, Portugal, where researchers show the greatest willingness to engage in pro bono peer review activities, with a ratio significantly higher than that of the UK, US, or China.
Declaration of competing interests – I declare that, to date, I have reviewed over 1,200 papers. Last year, Web of Science highlighted my personal profile as an exemplary case of peer review contributions. https://publons.com/announcement/#your-review-contributions-in-web-of-science
Pacheco-Torgal 