How Lead-time and Length Bias Affect Survival Time

How does lead-time and length bias affect survival time?
Most diseases, especially chronic conditions like cancer, can be detected through screening at an early stage or when symptoms manifest. The difference in detecting disease through screening and when symptoms manifest is lead time. It is the time difference between diagnosing disease using screening and without screening. Length bias is a phenomenon where a disease case with a better prognosis and has slow progress is more likely to be clinically identified than a disease with a poor prognosis but with faster progress (Chapter 12). Therefore, a disease condition diagnosed through screening is more likely to have a better prognosis compared to the average of all other cases. Length bias suggests that chronic conditions detected at screening have dissipated counts of less hostile lesions. They have a slow growth rate and may never reach a considerable size to be detected clinically without screening.
Lead time and length bias appear to positiv...