The term "optimism" refers to an emotional and psychological perspective on life. It is a positive frame of mind and means that a person takes the view of expecting the best outcome from any given situation. An optimistic person is one who sees the glass as 'half-full' instead of 'half-empty'. In psychology levels of optimism can be measured by use of the Life Orientation Test and Attributional Style Questionnaire. Levels of optimism (and its reverse pessimism) appear to have some links to heredity but are heavily influenced by health and environmental factors.