This article has a correction
- Patrick M Bossuyt, professor of clinical epidemiology (firstname.lastname@example.org)1,
- Les Irwig, professor of epidemiology2,
- Jonathan Craig, associate professor (clinical epidemiology)3,
- Paul Glasziou, professor of evidence based medicine4
- 1 Department of Clinical Epidemiology, Biostatistics and Bioinformatics, Academic Medical Centre, University of Amsterdam, Amsterdam 1100 DE, Netherlands
- 2 Screening and Test Evaluation Program, School of Public Health, University of Sydney, Australia
- 3 Screening and Test Evaluation Program, School of Public Health, University of Sydney, Department of Nephrology, Children's Hospital at Westmead, Sydney, Australia
- 4 Department of Primary Health Care, University of Oxford, Oxford
- Correspondence to: P M Bossuyt
- Accepted 11 March 2006
Evaluating diagnostic accuracy is an essential step in the evaluation of medical tests.1 2 Yet unlike randomised trials of interventions, which have a control arm, most studies of diagnostic accuracy do not compare the new test with existing tests.
We propose a modified approach to test evaluation, in which the accuracy of new tests is compared with that of existing tests or testing pathways. We argue that knowledge of other features of the new test, such as its availability and invasiveness, can help define how it is likely to be used, and we define three roles of a new test: replacement, triage, and add-on (fig 1).
Knowing the future role of new tests can help in designing studies, in making such studies more efficient, in identifying the best measure of change in accuracy, and in understanding and interpreting the results of studies.
New tests may differ from existing ones in various ways (table 1). They may be more accurate, less invasive, easier to do, less risky, less uncomfortable for patients, quicker to yield results, technically less challenging, or more easily interpreted.
For example, biomarkers for prostate cancer have recently been proposed as a more accurate replacement for prostate specific antigen. A rapid blood test that detects individual activated effector T cells (SPOT-TB) has been introduced as a better way to diagnose tuberculosis than the tuberculin skin test. Myelography has been replaced in most centres by magnetic resonance imaging to detect spinal cord injuries, not only because it provides detailed images, but also because it is simpler, safer, and does not require exposure to radiation (table 2).