|
To determine which
of two tests -- dobutamine echo or exercise ECG -- is preferable,
you must first calculate the post-test probability of disease
for each test.
In this case, the pre-test
probability of coronary artery disease is 0.25, which corresponds
to pre-test odds of 1:3. Now, recall Bayes' theorem:
Post-test odds =
pre-test odds x likelihood ratio
Click
for how to convert odds to probability
Click
for how to convert probability to odds
Analyze the table of
post-test probabilities below.
| Table
1.9.1: Post-test Probabilities
|
|---|
|
| Dobutamine
echocardiogram
| Exercise
ECG
|
|---|
|
pre-test odds | 1
in 3 | 1
in 3 |
post-test
odds
| | |
test positive
| 1.5
to 1 | 1
to 1 |
| test
negative | 1
in 20 | 1
in 7
|
post-test
p[CAD]
| | |
| test
positive | 0.60
| 0.50 |
| test
negative | 0.04
| 0.12 |
|
Question
1.9.1
Which test is preferable
and why?
 | Dobutamine
echocardiogram is the better test. |
 | The
exercise ECG is the better test. |
 | The
two tests are equally useful. |
 | Neither
test is useful. |
|