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(A) Length-time bias/length-biased sampling. Green lines, cancers picked up by screening; Red lines, cancers missed by screening; Dx, time when disease is clinically obvious without testing. (B) Overdiagnosis. *, lifespan unchanged. (C) Cancer overdiagnosis due to tumor heterogeneity. (Courtesy of H. Gilbert Welch, Brigham and Women's Center for Surgery and Public Health).
