Optimism is a mental attitude reflecting a belief or hope that the outcome of some specific endeavor, or outcomes in general, will be positive, favorable, and desirable. A common idiom used to illustrate optimism versus pessimism is a glass filled with water to the halfway point: an optimist is said to see the glass as half full, while a pessimist sees the glass as half empty. Optimism is a mental attitude reflecting a belief or hope that the outcome of some specific endeavor, or outcomes in general, will be positive, favorable, and desirable. A common idiom used to illustrate optimism versus pessimism is a glass filled with water to the halfway point: an optimist is said to see the glass as half full, while a pessimist sees the glass as half empty. The term derives from the Latin optimum, meaning 'best'. Being optimistic, in the typical sense of the word, is defined as expecting the best possible outcome from any given situation. This is usually referred to in psychology as dispositional optimism. It thus reflects a belief that future conditions will work out for the best. For this reason, it is seen as a trait that fosters resilience in the face of stress. Theories of optimism include dispositional models, and models of explanatory style. Methods to measure optimism have been developed within both theoretical systems, such as various forms of the Life Orientation Test, for the original definition of optimism, or the Attributional Style Questionnaire designed to test optimism in terms of explanatory style. Variation in optimism and pessimism is somewhat heritable and reflects biological trait systems to some degree. It is also influenced by environmental factors, including family environment, with some suggesting it can be learned. Optimism may also be linked to health. Researchers operationalize the term differently depending on their research. As with any trait characteristic, there are several ways to evaluate optimism, such as the Life Orientation Test (LOT). This 8-item scale was developed in 1985 by Michael Scheier and Charles Carver. Dispositional optimism and pessimism are typically assessed by asking people whether they expect future outcomes to be beneficial or negative (see below). The LOT returns separate optimism and pessimism scores for each individual. Behaviourally, these two scores correlate around r = 0.5. Optimistic scores on this scale predict better outcomes in relationships, higher social status, and reduced loss of well-being following adversity. Health preserving behaviors are associated with optimism while health-damaging behaviors are associated with pessimism. Some have argued that optimism is the opposite end of a single dimension with pessimism, with any distinction between them reflecting factors such as social desirability. Confirmatory modelling, however, supports a two-dimensional model and the two dimensions predict different outcomes. Genetic modelling confirms this independence, showing that pessimism and optimism are inherited as independent traits, with the typical correlation between them emerging as a result of a general well-being factor and family environment influences. It is suggested that patients with high dispositional optimism appear to have stronger immune system since it buffers it against psychological stressors. Explanatory style is distinct from dispositional theories of optimism. While related to life-orientation measures of optimism, attributional style theory suggests that dispositional optimism and pessimism are reflections of the ways people explain events, i.e., that attributions cause these dispositions. Here, an optimist would view defeat as temporary, does not apply to other cases, and is not considered his fault. Measures of attributional style distinguish three dimensions among explanations for events: Whether these explanations draw on internal versus external causes; whether the causes are viewed as stable versus unstable; and whether explanations apply globally versus being situationally specific. In addition, the measures distinguish attributions for positive and for negative events. An optimistic person attributes internal, stable, and global explanations to good things. Pessimistic explanations attribute these traits of stability, globality, and internality to negative events, such as difficulty in relationships. Models of Optimistic and Pessimistic attributions show that attributions themselves are a cognitive style – individuals who tend to focus on the global explanations do so for all types of events, and the styles correlate among each other. In addition to this, individuals vary in how optimistic their attributions are for good events, and on how pessimistic their attributions are for bad events, but these two traits of optimism and pessimism are un-correlated.