The initial Big Five Personality model was advanced by Ernest Tupes and Raymond Christal in 1961, but failed to reach an academic audience until the 1980s. In 1990, J.M. Digman advanced his five-factor model of personality, which Lewis Goldberg extended to the highest level of organization. These five overarching domains have been found to contain and subsume most known personality traits and are assumed to represent the basic structure behind all personality traits. At least four sets of researchers have worked independently for decades on this problem and have identified generally the same five factors: Tupes and Christal were first, followed by Goldberg at the Oregon Research Institute, Cattell at the University of Illinois, and Costa and McCrae (1985) at the National Institutes of Health. These four sets of researchers used somewhat different methods in finding the five traits, and thus each set of five factors has somewhat different names and definitions. However, all have been found to be highly inter-correlated and factor-analytically aligned. Measures for the big five personality traits are NEO Personality Inventory (NEO-PI), NEO Five Factor Inventory (NEO-FFI) and MMPI-2 (Demoralization scale for neuroticism).