Flowchart for test if negative series design. Flowchart depicts a test if negative series screening trial from an omniscient point of view. Dashed lines indicate a pathway that is unavailable to that class of participants (true case or true non-case) due to the assumptions of our model. In A, non-cases who screen positive on Test 1 are given a reference test. The results of this test are negative. The study investigator then goes on to screen the participant with Test 2, in case the reference test has failed. In B, cases who screen positive on Test 1 are given a reference test. The results of this reference test are positive and the study participant is observed to have disease. The gray box indicates cases that are misclassified as non-cases by the study investigator. The design is similar to that of Lehman et al. .