Q:

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.

A:

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.

A:

I would say that the use of self-citations that you describe is very common, but whether it's dirty is not clear-cut and it's probably difficult to study. I can also see several different perspectives, some more malicious than others: 

Bias due to better knowledge of your own and related researches (friends) work. I find this rather benign, often unintential and natural. 
When providing a reference to support a specific point, everything else equal, most researchers will probably cite their own work before the work of others. This with the assumption that both papers provide equally good evidence/arguments, and that the author can only use a maximum number references for his paper (which is commonly the case). This behaviour is probably most often seen in soft/weak references of general points in e.g. introductions and discussions. I personally find this behaviour maybe not ideal, but rather human.
The concious choice not to cite other researchers work that would be relevant. This can come in (at least) two forms: 1) ignoring researchers with a critical perspective on your work (~academic feud), 2) wanting to "claim" the field as your own. Both of these cases should ideally be spotted during the review process, but I think it is very common so still see traces of them in published papers. The problem is probably to prove bad intent, and it is also dependent on reviewers that know the litterature in the specific field extremely well and also bother to speak up about it. This form of behaviour is naturally the most problematic one.

Under point 3, the first form (ignoring criticism) has recieved most attention. However, reading between the lines, I feel that the second form is relatively common as well, where groups of researchers try to "claim" a specific topic (intentionally or unintentionally), so that their body of work is the go-to reference for this topic. A good way to achive this would be to preferentially cite work from within the group, especially if you are already a well established researcher. This can be particularly powerful if you are writing review papers of topics, since these can be used to define the core literature of a topic for future researchers that discover the field (probably related: Matthew effect).
I don't know about studies that try to quantify how common these specific behaviours are. However, the study of citation patterns and self-citations is common, and two papers that touch upon the things mentioned here are Hyland (2003) and Fowler & Aksnes (2007). Hyland (2003) looks at how self-citations can be used for different purposes, while Fowler & Aksnes (2007) tries to quantify the "value" of self-citations (which seems to be quite large).

