In this paper, we study the citation decision of a scientific author. By citing a related work, authors can make their arguments more persuasive. We call this the correlation effect. But if authors cite other work, they may give the impression that they think the cited work is more competent than theirs. We call this the reputation effect. These two effects may be the main sources of citation bias. We empirically show that there is a citation bias in Economics by using data from RePEc. We also report how the citation bias differs across regions (U.S., Europe and Asia).