1, the data and model on which the extrapolation depends have errors, which affect the accuracy of the results.
2, human behavior and environmental factors are difficult to predict and control completely, such as personal living habits, social and economic development and other factors will have an impact on health.
3. Individual difference is also an important uncertain factor, and everyone will have different reactions when encountering the same disease or intervention measures.
4. In the long-term extrapolation, we need to consider the changes brought by emerging technologies and medical progress, which will change the applicability of the original model.