Figure 1

Paired screening trial flowchart. Trial design, and observed and true outcomes for a paired screening trial of two continuous tests, with two possible secondary tests used determine disease status. Cases of disease which escape detection during the study appear in the shaded oval. The study investigator will miss cases of disease when 1) no signs or symptoms are observed; 2) the less sensitive secondary test is used; and 3) the participant has disease. One or both screening tests may cause a participant without disease to be recalled. By assumption, the invasive, sensitive and specific secondary test will never diagnose disease when there is in fact no disease. Thus, the study investigator never declares a participant to have disease when in fact they do not.