Availability of digital object identifiers in publications archived by PubMed

Digital object identifiers (DOIs) were launched in 1997 to facilitate the longterm access and identification of objects in digital environments. The objective of the present investigation is to assess the DOI availability of articles in biomedical journals indexed in the PubMed database and to complete this investigation with a geographical analysis of journals by the country of publisher. Articles were randomly selected from PubMed using their PubMed identifier and were downloaded from and processed through developed Hypertext Preprocessor language scripts. The first part of the analysis focuses on the period 1966-2015 (50 years). Of the 496,665 articles studied over this period, 201,055 have DOIs (40.48%). Results showed that the percentage of articles with DOIs began to increase for articles published in the 2000s, with spectacular growth in the years 2002-2003, then reached a peak in 2015. Data on countries showed that some countries gradually implemented DOIs over the period 1966 to 2015 (the United States, the United Kingdom, and the Netherlands), while some did not (Russia, the Czech Republic, and Romania). The second part of the analysis focuses on the year 2015 and includes 268,790 articles published in 2015, randomly selected to evaluate the current implementation of DOIs. In 2015, 86.42% of articles had DOIs. The geographical analysis of countries of publishers showed that some countries (Russia, Thailand, and Ukraine) still assigned few DOIs to articles in 2015. Thus, if the scientific community aims to increase the number and the usefulness of services rendered by DOIs, efforts must be made to generalize their use by all persons involved in scientific publication, particularly publishers.