Final answer:
Self-descriptions of adults in midlife tend to be more positive compared to those of younger adults, and this positive self-perception can contribute to increased longevity. The stability of these self-descriptions is influenced by social and economic factors.
Step-by-step explanation:
The self-descriptions of adults in midlife are generally considered to be more positive than those of younger adults. Research, such as the work by Levy et al. (2002), has indicated that positive self-perceptions can have a beneficial impact on longevity. As individuals age, they often gain a more stable sense of self, which contributes to a positive outlook on life. Additionally, it's important to consider the social and economic context, as there is an indication from various studies, including Logan, Ward, and Spitze (1992), that in economically developed countries, the demographic structure leans towards having fewer middle-aged individuals and more young individuals compared to undeveloped countries.