Sometime in literature, theories and models are not distinguished among themselves very well, which makes it harder to understand. In a way, theories are more specifications of the process involved for a particular phenomenon. It"s a set of ideas to explain something. Models on the other hand specify categories of variables that should be related/ representing the theory: aging is usually defined as, death is the final event. Theories of aging: since the beginning, the aging process happens at the biological, psychological and social levels. They start with getting facts and try to group them into models and hardly achieve the status of theory. Gender is one of the strongest predictors of life expectancy with women living the longest. Deviation amplification mechanisms: developed by maruyama in 1963 argued that systems (homeostasis: heart rate, blood pressure, respiratory rate) can and do change over time.