Final answer:
Chronic illness is the factor that is not linked with being in the 'happy-well' group between ages 75 and 80. Instead, regular physical exercise, social engagement, and a positive emotional outlook are contributing factors to wellbeing in older age.
Step-by-step explanation:
The factors at age 50 that were linked with being in the "happy-well" group at age 75 to 80 years of age included regular physical exercise, social engagement, and a positive emotional outlook. However, chronic illness is not linked with being in the 'happy-well' group and hence is the correct answer to the question. A healthy lifestyle, incorporating regular physical activity and social connections, enhances longevity and wellbeing. Optimism and physical health also have a positive correlation, contributing to a better quality of life in older age.