Background
In response to the potential impacts on the economic, medical, family and social aspects of population aging, one of the former institutes of the Health Promotion Administration, the Institute of Family Planning, started to plan for studies on the elderly in 1987. The baseline survey of Taiwan Longitudinal Study on Aging , also known as TLSA, was conducted on a nationally representative sample of adult residents aged 60 and above in non-aboriginal townships of Taiwan in 1989. 
Afterwards, the respondents have been followed every three to four years. In 1996, 2003 and 2015, refresh cohorts aged 50 and above were sampled to maintain representativeness of the younger population. In 2015, a new nationally representative sample of adult residents aged 50 and above in Taiwan was selected.The most recent follow up survey was conducted in 2023.

Aim of the Study
The specific aims of this survey are:
1. To understand the health status and wellbeing of the middle-aged and elderly in Taiwan, including physical function, disability, illness, mental health, health behavior,and the utilization of preventive health care.

2. To understand the social status of the middle-aged and elderly in Taiwan, including family structure, living arrangements, social support, leisure activity, socioeconomic status, life satisfaction, occupation and retirement, and awareness and utilization of services provided by the government.

3. To compare the differences of health and social status among subgroups of people characterized by their socio-economic background.

4. To explore the needs of the middle-aged and elderly on health care or supports for healthy living.

Sampling and Survey Method
For the baseline survey conducted in 1989, household registration data of residents aged 60 and above in non-aboriginal townships in 1988 were used as sampling frame for this study. A three-stage systematic random sampling method was used for the selection of an equal probability sample. Afterward, two fresh samples were selected in 1996 and 2003 in order to maintain representativeness of the younger age cohort and extend representativeness of the sample to the population aged 50 and above.

As attrition occurred during years of follow-up, a new cohort comprising of respondents from both the non-aboriginal and aboriginal townships was established in 2015. 
Data were collected with face-to-face interview questionnaires by trained interviewers.

Content of the Survey
The contents of the questionnaire:

1. Personal information, marriage and residence history, religious beliefs.

2. Household structure, satisfaction with living arrangements, interaction with 
   children, relatives and friends, etc.

3. Health, utilization of medical services and hygiene behaviors: self-assessment of health, cognitive        function, illness status, pain, falls, activities of daily living and  disability, utilization of healthcare            services, nutritional intakes, health care behavior, source of stress and mental depression,                    well- being, life satisfaction, loneliness, health information acquisition, health literacy, vaccination          status, etc.

 4. Social support and exchange: provides or receives support from family members.

5. Work history: personal current work situation, retirement planning and future work intentions.

6.Social participation and physical safety: types and frequency of participation in social groups and political activities, senior learning, and physical safety 
   (secure living domain).