<prompt> Lead time refers to the time betweenDisease onset and final critical diagnosisDisease onset and final possible point of detectionFirst possible point of detection and final critical diagnosisFirst possible point of detection and usual time of diagnosis  <response>: LEAD TIME is the advantage gained by screening, i.e., the period between diagnosis by early detection and diagnosis by other means. It is an impoant factor when evaluating the effectiveness of a specific test. Ref: 25th edition, Parks Textbook of Preventive and Social Medicine, Page no. 148 