Figure 1.

Screening for lung cancer. Hypothetical results are shown for A = spiral CT, B = x-ray, and C = no screening. In the sequential study, results for B and C are similar in the first trial (when 30% of the subjects receive the new therapy), and results for A and B are similar in the second trial (when 70% of the subjects receive the new therapy). However, as shown with three-arm trial, it is incorrect to make the transitive inference that when 70% of the subjects receive the new therapy, the results for A and C would be similar.

Baker and Kramer BMC Medical Research Methodology 2002 2:13   doi:10.1186/1471-2288-2-13
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