You can not directly measure the life expectancy of elderly. The starting point for calculating life expectancy is the age-specific death rates of the population members. Generally it is calculated using indirect techniques of estimation of life expectancy. Its a little bit complicated.
Thanks for your advice. But I want to assess how the elderly hope to their current life, not about the age-specific death rates of the population members.
There are a number of methods for determining LE using demographic methods and models such as the Sullivan method based on a standard period life table. You might be interested in this paper, "Inequality in disability-free life expectancies among older men and women in six countries with developing economies". www.ncbi.nlm.nih.gov/pmc/articles/PMC5013163/
Dear that will not be life expectancy but actually an estimation of hope or will of the elderly about the time period they want to live alive .That will again vary among the healthy and sick elders .I there recommend you to divide your study into two groups 1. 1. Healthy elders
2.Sick elders
Then compare the two groups that will draw a good conclusion
Even the disease group can be sub-divided on the bases of diseases
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