Almost all papers these days have a DOI and it is worth know­ing how to use them.

At the top or bot­tom of the first page of a paper, you will see some­thing like this:

doi:10.1016/j.csda.2006.07.028

This is a unique and per­ma­nent iden­ti­fier for the paper known as a “Dig­i­tal Object Iden­ti­fier”. The part before the for­ward slash (10.1016 in the exam­ple above) iden­ti­fies the nam­ing author­ity (in this case Else­vier) and the part after the for­ward slash (j.csda.2006.07.028) iden­ti­fies the par­tic­u­lar paper. In this case, the paper iden­ti­fier shows it is in the jour­nal Com­pu­ta­tional Sta­tis­tics and Data Analy­sis and that it first appeared online in 2006. How­ever, there is no sys­tem­atic pat­tern to these iden­ti­fiers, and other jour­nals use other ways of gen­er­at­ing identifiers.

One use for these num­bers is that it pro­vides a quick way of find­ing the paper online. The URL http://dx.doi.org/xxx where xxx is the DOI will lead to the paper. For exam­ple, http://dx.doi.org/10.1016/j.csda.2006.07.028 gives the above paper.

A URL gen­er­ated in this way is usu­ally much shorter than other equiv­a­lent URLs, and is guar­an­teed not to change, even when the pub­lisher reor­ga­nizes their web­site. For some jour­nals, the URL of an arti­cle may change when the arti­cle moves from being online but not yet allo­cated to an issue, to being part of a print issue. But the DOI will remain the same regard­less. That is why I usu­ally pro­vide links of this form to my online pub­li­ca­tions from my website.