Psychologists often use the 'Big Five' or OCEAN model to assess people's personality on five variables: Openness, Conscientiousness, Extraversion, Agreeableness and Neuroticism (the tendency to see events in a negative or pessimistic light). Previous research has linked extraversion to a decreased risk of depression and neuroticism to an increased risk but there has been little or no research into all five factors. Researchers from Virginia Commonwealth University in Richmond, Virginia studied 44,112 people including 542 pairs of twin - something which allowed them to explore the links between personality type, genetics and depression. They found that neuroticism was the most-important personality factor in influencing the link between genetics and depression. The next most important factor was conscientiousness - the less conscientious people were the more likely they were to become depressed. Openness, extraversion and agreeableness all had less of an influence.
Kendler, K.S. and Myers, J. - The genetic and environmental relationship between major depression and the five-factor model of personality Psychological Medicine May 2010, 40(5), 801-806