What type of bias occurs when screening detects a disease earlier, lengthening the time from diagnosis to death?

Lead-time bias occurs when screening methods identify a disease earlier than it would have been recognized without screening, effectively prolonging the time a patient is aware of their diagnosis. This bias can create the illusion that survival rates have improved simply because the disease was detected sooner, not because the overall prognosis has changed. Patients whose diseases are caught by screening often seem to live longer from the time of diagnosis, even though their actual life expectancy may remain unaffected. This phenomenon can mislead clinicians and researchers interpreting survival data, suggesting that the screening led to better outcomes when, in fact, the time from diagnosis to death has merely been stretched due to earlier detection.

In contrast, the other types of bias mentioned relate to different contexts. Observer bias pertains to perceptions of the investigator influencing results; detection bias involves discrepancies in how outcomes are recorded or detected based on patient characteristics; and attrition bias refers to loss of participants in a study affecting the results. Each of these biases operates under different circumstances, demonstrating that lead-time bias specifically addresses the effects of earlier diagnosis due to screening.