Question: I am a newly appointed editor to a top journal. I have received my first manuscript assignment. I see in the journal system that the authors have provided preferences for reviewers for their paper.

I was wondering what is the norm like with respect to this. Do editors normally go by author's preference or do they ignore it? What factors should I take into account before considering author preference of reviewers?

On one hand this makes my task of searching appropriate reviewers easy but I suspect this might also give an unfair edge to the authors if the reviewers have some/any kind of bias.

Answer: 
The way the preferred reviewers are used varies. Some go by these suggestions whole-heartedly while others do not. I lean towards the latter since my experience with some preferred names is less than favourable.

In my experience names listed can be good. I usually double check to see if persons seem affiliated in some way and if they do I avoid appointing them. As a rule, however, I try to find persons independently and based on my own experience. I tend to use the preferred names as back-ups unless my preference and the authors coincide.

The reason for my slight aversion towards the preferred is that some authors tend to list friends and other persons who are obviously close to the authors. I have seen many low quality reviews come out from such reviewers an clearly at a rate very different from independently chosen reviewers. Judging what is too close is not easy and sometimes it may be justified if, for example, the topic is such that local knowledge comes into play. For the reason of uncertainty I therefore try to at least mix them up so that one is chosen by me independently and the other is selected from the authors suggestions.

So, try to assess the quality of the preferred reviewers and at least try to find some to complement a preferred reviewer will be my advice.

It is also common that authors list non-preferred reviewers. I always stay clear of such reviewers since I do not know what lies beneath the sentiment.
Be extra careful when following authors' suggestions for suitable peer reviewers. There has been a recent case of authors suggesting fabricated contacts as "reviewers", as described on <http://publicationethics.org/news/cope-statement-inappropriate-manipulation-peer-review-processes>. That case led some publishers to stop asking for reviewer suggestions explicitly within their submission processes.

Measures of caution that I find useful include:

* Only choose an author-suggested reviewer if you can verify independently that this person is suited as reviewer, ideally from your own prior knowledge.
* Don't use the contact address provided by the authors, but use a contact address that you can obtain independently, for example from the reviewer's university web page.
* Verify very carefully that there's no conflict of interests for that reviewer, for example joint publications, same affiliations also in the recent past, or similar.
* Don't make a decision if you only have reviews from author-suggested reviewers, but have at least one independently chosen reviewer.