What is Accuracy when it comes to biochemical testing?
how close the result is to the true value
What is precision when considering biochemical testing?
How often the same result is found when repeated - not necessarily accurate!
When might you get a false positive?
When the normal for that person falls outwith the reference interval for that test
the percentage of people with a disease who have a positive result
the percentage of people without a disease that test as having a normal parameter
The positive predictive value is...
% of people who have a positive test who have the disease
The negative predictive value is...
% of people with a negative test that don't have a disease
% of people tested who have the disease
TP + FP/TP+FP+TN+FN
measure of how common the disease is in the population of people who have been tested
What does prevalence affect?
Positive Predictive Value
Negative Predictive Value
As prevalence falls...
a. PPV falls
b. NPV falls
As prevalence falls, PPV falls and NPV rises
What remains the same regardless of prevalence?
sensitivity and specificity
When are tests most useful?
When a disease is has more than 50% prevalence
Why is troponin useful in diagnosing an MI?
because the heart is the only tissue that produces it