Summary. Multiphase (stage) designs that involve more than two phases are increasingly used by clinicians and psychologists for diagnosis and screening of dementia and many other diseases, e.g. colorectal or breast cancer. The multiphase design is an extension of the commonly
used two‐phase design, where an inexpensive initial screening test is followed by a gold standard. In a typical three‐phase design, the screening test in phase 1 usually has high sensitivity but relatively low specificity. Phase 2 consists of a repeated application of the initial
screening test and/or a more confirmatory test and then the gold standard test is used in phase 3. In such designs, both the verification process and the accuracy of each screening test may depend on patients’ characteristics. In addition, multiple‐screening tests are correlated
and composite decision rules may be used. However, no estimation methods exist for assessing the accuracy of a multiphase diagnosis procedure. To address these problems, we develop a method of estimating the diagnostic accuracy for each individual test and for the whole diagnostic procedure
in a multiphase design in the presence of verification bias. Simulation studies are carried out to evaluate the performance of the method proposed and to compare different strategies of combining sequential tests. The method proposed is applied to data from a multiphase study of dementia.