Overall Diagnostic Accuracy is dependent on the Prevalence and Provides Clinically Important Information.
Overall Diagnostic Accuracy is dependent on the Prevalence and Provides Clinically Important Information.
| Prior Suspicion of Coronary Disease | |||
|---|---|---|---|
| Low | Intermediate | High | |
| Prevalence | 5% | 50% | 90% |
| A | 30 | 300 | 540 |
| B | 86 | 45 | 9 |
| C | 20 | 200 | 360 |
| D | 864 | 455 | 91 |
| Overall detection accuracy | 0.711 | 0.711 | 0.711 |
| Overall diagnostic accuracy | 0.894 | 0.755 | 0.631 |
The original data were provided by Sackett et al.6(p94) (in their book, Table 10) in a study of 350 patients with a prevalence of 227/350=64.86%. In that study, a=137, b=11, c=90, and d=112. Thus, the sensitivity is 60.35% and the specificity is 91.06%, and the calculated “overall detection accuracy”=71.1 and is constant, regardless of the prevalence in the three populations. However, the overall diagnostic accuracy, which changes for each population based on the prevalence (and Bayes’ rule), is more informative.