Final answer:
Longitudinal life expectancy data are complex, as they cannot easily account for the individual choices or healthcare investments that contribute to health outcomes.
Step-by-step explanation:
The downfalls of longitudinal life expectancy data include the challenge that it is almost impossible to distinguish whether health outcomes such as life expectancy were the result of personal preferences that might affect health and longevity, such as diet, exercise, certain risky behavior, and consumption of items like tobacco, or the result of health care expenditures, like annual check-ups. In addition, limitations of longitudinal research include the substantial time and financial investment required, which can restrict the ability to conduct comprehensive studies. Furthermore, changes in societal factors, medical technology, and healthcare practices can impact the outcomes and relevance of such data over time.