Lead time is defined is ?
Ans. is 'b' i.e., Time between point where the diagnosis is made by screening test to usual diagnosis In respect to screening test and diagnostic test, a disease passes through following phase, sequentially. Disease onset - Disease process just staed. First possible point of diagnosis - The earliest point in disease process where a diagnosis can be made, i.e., before this point diagnosis can not be made by any test. Final critical point of diagnosis - The point after which even diagnosis and treatment will not change the outcome. Usual time of diagnosis - Time in disease process when most of the people are diagnosed by usual diagnostic procedure (not screening test).