When PLOS ONE hiccups, everyone notices. For smaller journals, a sudden drop in publication output in a single month may raise some eyebrows, but is usually explained by unpredicable events–unseasonably nasty weather, an editor of a special issue frustratingly behind schedule, a few authors not returning revisions in short order, for example. But for very large journals, like PLOS ONE, which published more than 31,000 articles in 2013 alone, stochastic events tend to dampen themselves out. Bad weather is regional; one tardy editor among more than 5,000 other editors is hardly noticed; a few late authors makes even less of a difference. PLOS ONE is playing a very large numbers game, so a sizable decline in published papers signals a structural shift and not a random blip.
In 2014, publication output in PLOS ONE dropped by 12%, from 3019 published papers in January to 2657 in February. While this drop represents a decline of 362 papers in a month with just 28 days, publication output increased 3% during this same period in 2013 (from 2367 to 2427), and 30% in 2012 (from 1292 to 1679).
In a post written last June, just after PLOS ONE received its 2012 Impact Factor (3.730), I predicted that authors would start moving away from the multidisciplinary megajournal and start returning to disciplinary-based publication. It would just take a few months to start seeing that trend.
We may be seeing the leading edge of that trend.
Based on an analysis of the first 500 PLOS ONE papers published in February 2014, the median number of days from submission to publication was 151 days (Interquartile Range (IRQ): 117 to 188 days), meaning about 5 months of delay with the middle half (25th to 75th percentile) of the papers being published within 4 to 6 months of submission. The main source of delay was the period from submission to acceptance–a median of 111 days (IRQ: 80 to 148), almost 4 months, while acceptance to publication took a median of 35 days (IRQ: 31 to 45). Editors please take notice of what you are competing against.
Is publication of the 2012 Impact Factor the likely cause of the decline?
The Journal Citation Report, which includes the annual Journal Impact Factor, was published on June 19, 2013. Based on their date of submission, 87% (435 of 500 papers) were submitted after PLOS ONE’s Impact Factor was announced. The median date of submission for this sample of articles was September 5, 2013. Even if it took a couple of weeks for news of the new Impact Factor to circulate, the majority of authors knew (or could have known) PLOS ONE’s new Impact Factor.
This simple explanation, that authors are moving to higher-performing journals, is not entirely supported by the data, however. Publication increased by 5% at the end of 2013, from 2904 in November to 3041 in December, but fell by 1% in January 2014 to 3019. Ultimately, we can never know what the trend would be if PLOS ONE’s Impact Factor stayed above 4, yet I’m at a loss to find other causes of the recent downward trend.
Authors are sensitive to Journal Impact Factors, and PLOS ONE authors are no different, as PLOS’s own analysis suggests. If the numbers reported reflect the bulk action of thousands of submitting scientists, the data suggest a mass movement away from PLOS ONE toward higher performing mid-tier journals. As the 2013 Impact Factor (due in June, 2014) is predicted to drop PLOS ONE even further , we may be witnessing the beginning of a very large shift in manuscript flow.
UPDATE: See PLOS ONE Output Falls 25 Percent for more recent data.
 James Hardcastle, Research Manager of the Taylor & Francis Group, predicts PLOS ONE’s 2013 Impact Factor will be between 3.1 and 3.2.