The legal understanding of any publication, irrespective of the number of authors, is that each has contributed equally in the work involved. Eventually, scores are calculated on the number of times a paper is read and/or quoted. So, it should make no difference to an individual's score whether their publication in an indexed journal is a single or multi-authored one. A couple of things to be said: It no longer makes a difference who the first or last author is; in fact, some of us have taken to putting our names first when we are the senior authors, as that is the name in abbreviated references. Secondly - and more importantly - we all need to be careful about the names on a publication. All indexed journals will ask each author to sign to the veracity of the publication. This is particularly relevant with "Big Data" that we now find. I.e. If one has neither contributed to the work, nor knows the data or doesn't agree with the data, then it is inappropriate to allow one's name to be added on. More than scores, rules around plagiarism have become even more important. I would advice authors to always be careful about whom they invite to add their names on to individual work. (p.s. I apologise if I haven't answered the question precisely, but I have taken the opportunity to remind people that as doctors our ethical responsibilities in publishing must always remain at the forefront.)