Another important factor when considering major depression is related to the risk of an individual harming themselves. Women have a much higher rate of attempting to kill themselves, but men have a much higher rate of completing the act due to the more lethal means which they use (guns and hanging as compared medication overdose or wrist cutting).  The highest risk associated for people actually killing themselves is among the separated, divorced and recently widowed, with lowest risk being for single and married individuals.  Living alone or living in an urban environment also conveys a greater risk than cohabiting or living in a rural area.  Also, individuals with families showing a history of family member's harming themselves or a history of alcoholism and major depression, or those who perceive that they do not have a good social network are at greater risk. 

Although heritability rates are greater for bipolar disorders than for individuals with unipolar major depression, there is some evidence that there may be some biological inheritance or predisposition. The concordance rate (heritability rate) for monozygotic twins for major depression is about 50%, whereas the concordance rate for dizygotic twins is about 35%. Various studies estimate the overall heritability rate for major depression and about 39%, indicating some biological predisposition, but also reflecting the likelihood that other social and environmental factors (such as life events, developmental history and coping skills) are probably even more prominent.  Studies of adopted twins with depression have found the rates for major depression in biological and adoptive parents to reflect only a small effect of heredity. 

Information provided by Leahy and Holland’s Treatment Plans and Interventions for Depression and Anxiety Disorders