Is citation bias a studied issue? I have noticed in a number of papers, including those in top journals, a common dirty practice which consists of self citing your previous works and omitting other important references in the area (I admit some of them at least include the classic references). For instance Prof. John Doe writes a paper and his references look like:

[1] John Doe (1970). Paper 1.
[2] John Doe (1971). Paper 2.
...
[200] John Doe (2014). Paper 200.
[201] Issac Newton (1687). Philosophiæ Naturalis Principia Mathematica.

I am aware of the concept of Publication Bias, which is related to a bias with regard to what is published. I wonder if there is also something related to self-citation bias or citation bias (it might also be the case that a person only cites a group of researchers (friends?))?
This, of course, is not just a matter of taste, but it is a practice that complicates the literature review in a certain area.
This problem has been receiving significant attention in recent years.  Among other thing, there was a recent scandal around "citation cartels", in which journal editorial staff organized not only to ensure their own journals self-cited but also so that groups of conspirator journals would cite one another in order to raise impact factor while adding a layer of indirection to make it harder to track.  Such journals also sometimes strong-arm authors into adding citations to other publications within the same journal.

I don't know if anybody has tried to further tease apart the different between intentional (i.e., citation cartel) and unintentional citation bias.  It would be interesting to study, but may be difficult given the amount of intentional bias that some are using the game the system.