Background: The reference standard for measuring diagnostic test accuracy ideally should be error-free in establishing the diagnosis of the condition of interest and should be applicable to all of the population being tested. Unfortunately it is virtually impossible to find such reference standards to measure the accuracy of diagnostic imaging (DI) tests.
Objective: the objective of this presentation is to describe and illustrate the principal barriers to finding an ideal reference standard for assessing DI test accuracy.
Analysis: there are three main barriers to finding an ideal reference standard for assessing the accuracy of DI tests.
1. The high quality of current DI technology. Pathology is usually considered to be the ideal reference standard for assessing DI test accuracy. However, DI very often provides imaging of pathology which is as good as anatomical pathology. Common examples would be fractures, gallstones, appendicitis and intracranial hemorrhage.
2. The reference standard cannot ethically be applied to all study participants. One of the most common uses for DI is to diagnose conditions, such as tumours, injuries or abscesses, which require surgical intervention. The findings at surgery are an excellent reference standard. However, surgery can only ethically be performed on those patients with a positive DI test.
3. There is no practical reference standard for the condition being assessed. Examples of this would include such common conditions as pneumonia and pulmonary oedema for which DI is one of the primary diagnostic tests.
Conclusion: finding a reference standard for assessing DI test accuracy is extremely difficult. Methodologists and radiologists need to work together to establish appropriate criteria for determining reference standards for assessing DI test accuracy.