To calculate health expectancies with the method of Sullivan also implies to make some approximations on the term of life. There are two problems:
Obviously, is not precisely known . More generally, quantification of mortality above the age of 80 and evaluation of survival at these ages raise substantial problems. A number of methodological and practical difficulties are involved. Most important of them are methodological and practical deficiencies of the measurement of old age mortality. For example, errors in data play much more serious role in the case of the elderly than in other bigger groups of the population. Errors are present in both the death and population statistics .
However, the biases are generally small compared to the standard errors and can safely be ignored in most cases.