Table 1. Traditional epidemiological study design and diagnostic efficacy hierarchies.
| Classification | Definition |
| A. Study design | |
| Case report | The presentation of one or two new cases |
| Case series | The presentation of three of more new cases |
| Cross-sectional | A prevalence study; observations related to one moment in time |
| Case–control | Subjects are classified on the basis of outcome (e.g. disease or no disease) and previous events (e.g. exposed or non-exposed). It is an attempt to link aetiology with their current disease status |
| Cohort | Subjects are classified on the basis of exposure and followed through time to see if an outcome develops or not. At least two observational points are chosen. This is an attempt to establish cause and effect |
| Experimental | Clinical trials with non-random and random allocation. Variables could be manipulated |
| B. Efficacy levela | |
| 1. Technical | Technical aspects of radiology equipment; comparison of radiographs based on the technical criteria, such as resolution, modulation, grey-scale range and sharpness |
| 2. Diagnostic accuracy | Yield of normal or abnormal diagnoses in a group of cases; assessed with sensitivity and specificity, predictive values or ROC analysis |
| 3. Diagnostic thinking | Number of cases in which an image judged helpful in making a diagnosis. Clinician changes diagnosis based on pre- and post-test information |
| 4. Therapeutic | Number of times the image was helpful in planning patient management. The number of times planned therapy was changed after test information was obtained |
| 5. Patient outcome | Number of patients improved with test vs without test; morbidity avoided; changes in life expectancy; cost saved with image information |
| 6. Societal efficacy | Cost/benefit from a societal viewpoint |
ROC, receiver operating characteristic. aModified from Fryback and Thornbury16