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. 2018 Mar 20;5:180043. doi: 10.1038/sdata.2018.43

Table 1. Details of the PubMed Central Open Access articles used as a citing universe.

  Articles (n = 1,152,905) Research Other
Articles (n = 1,152,905) 691,527
461,378
Articles with references 669,714 (97%)
329,969 (72%)
All With PMIDs All With PMIDs
# References 27,218,513 21,130,489 12,594,333 9,563,297
Average # references        
All articles 39.4 30.6 27.3 20.7
Articles with references 40.6 31.6 38.2 29.0
Articles with references in methods 596,627 (89%)
18,401 (6%)
All With PMIDs All With PMIDs
# References in methods 4,734,310 3,230,941 193,310 138,650
Average # references        
All articles 6.8 4.7 0.4 0.3
Articles with refs. in methods 7.9 5.4 10.5 7.5