A short loneliness scale was developed for use in large-scale surveys, consisting of three items and simplified response categories. The scale effectively measures overall loneliness and was validated in two population-based studies. The study found that objective and subjective isolation are related, but the relationship is modest, indicating that quantitative and qualitative aspects of social relationships are distinct. Loneliness is a key aspect of aging and is influenced by both objective and subjective factors. The three-item scale showed good reliability and validity, and it can be used in both in-person and telephone interviews. The study also confirmed the association between social ties and loneliness, highlighting the importance of studying both dimensions of social relationships in aging. The findings suggest that loneliness is a complex experience involving social isolation, absence of companionship, and rejection by peer groups. The study underscores the need for integrated research across social, psychological, and biological levels to understand aging well. The three-item scale provides a practical tool for measuring loneliness in large-scale surveys, enabling comparisons with other studies. The research highlights the importance of considering both objective and subjective measures of social isolation in understanding the impact of social relationships on well-being in later life.A short loneliness scale was developed for use in large-scale surveys, consisting of three items and simplified response categories. The scale effectively measures overall loneliness and was validated in two population-based studies. The study found that objective and subjective isolation are related, but the relationship is modest, indicating that quantitative and qualitative aspects of social relationships are distinct. Loneliness is a key aspect of aging and is influenced by both objective and subjective factors. The three-item scale showed good reliability and validity, and it can be used in both in-person and telephone interviews. The study also confirmed the association between social ties and loneliness, highlighting the importance of studying both dimensions of social relationships in aging. The findings suggest that loneliness is a complex experience involving social isolation, absence of companionship, and rejection by peer groups. The study underscores the need for integrated research across social, psychological, and biological levels to understand aging well. The three-item scale provides a practical tool for measuring loneliness in large-scale surveys, enabling comparisons with other studies. The research highlights the importance of considering both objective and subjective measures of social isolation in understanding the impact of social relationships on well-being in later life.