1. Uncertainty in Medical Testing

2. What is a false positive?
In forensic testing there are 4 possible outcomes to a test
The test for y is positive and the person has y **true positive
The test for y is negative and the person doesn’t have y **true negative
The test for y is positive and the person doesn’t have y **false positive
The test for y is negative and the person has y **false negative

3. Why does this matter
What if a doctor were to give a patient a prescription for an antibiotic due to a false positive strep test?
What might this contribute to (long term)?
Or worse…what if the doctor were to instruct the patient to self-manage mononucleosis due to a false negative test?
What are the risks here?

4. Sensitivity and Specificity
Sensitivity: the measure of how often a test will detect a condition when the condition is, in fact, present (true positive)
If you have 100 people with a condition and 95 of them test positive, the test has a sensitivity of 95%
Specificity: the measure of how often a test will give a negative result when the condition is not present
If you have 100 people without a condition and 98 of them test negative, the test has a specificity of 98%

5. Sources of Error Natural variability to biological processes
E.g. a test looking at antibodies in a person who may have a weak immune system
Human error
Failure to follow SOP, inexperience, etc.
Instrumental error
Machine not calibrated correctly, etc.