  It may seem surprising that, out of all areas of science, computer scientists
have been slow to post electronic versions of papers on sites like arXiv.org.
Instead, computer scientists have tended to place papers on our individual home
pages, but this loses the benefits of aggregation, namely notification and
browsing.
  But this is changing. More and more computer scientists are now using the
arXiv. At the same time, there is ongoing discussion and controversy about how
prepublication affects peer review, especially for double-blind conferences.
This discussion is often carried out with precious little evidence of how
popular prepublication is.
  We measure what percentage of papers in computer science are placed on the
arXiv, by cross-referencing published papers in DBLP with e-prints on arXiv. We
found:
  * Usage of arXiv.org has risen dramatically among the most selective
conferences in computer science. In 2017, fully 23% of papers had e-prints on
arXiv, compared to only 1% ten years ago.
  * Areas of computer science vary widely in e-print prevalence. In theoretical
computer science and machine learning, over 60% of published papers are on
arXiv, while other areas are essentially zero. In most areas, arXiv usage is
rising.
  * Many researchers use arXiv for posting preprints. Of the 2017 published
papers with arXiv e-prints, 56% were preprints that were posted before or
during peer review.
  Our paper describes these results as well as policy implications for
researchers and practitioners.
