Applied epidemiology in clinical practice Flashcards
How can validity be assessed
Specificity, sensitivity and positive predictive value
Describe positive predictive value
Positive Predictive Value (PPV) = The probability that a patient that tests +ve actually has the disease
Describe negative predictive value
Negative Predictive Value (NPV) = The probability that a patient that tests -ve actually doesn’t have the disease.
Describe the cervical screening test
Looks for the presence of HPV
If present, further cytological investigations to look for potential cancers
Introduced in 2016, with plans to be available in all areas of the UK by 2020.
What is the most common cancer for women aged under 35
Cervical cancer
Describe specificity
The ability of a clinical test to correctly identify those WITHOUT the disease (true negatives). ▪ I.E. 80% specificity means 80% are identified without the disease (true negatives) but 20% are identified as false positives.
Describe sensitivity
The ability of a clinical test to correctly identify those WITH the disease (true positives). ▪ I.E. 80% sensitivity means 80% are identified with the disease (true positives) but 20% are undetected with false negatives.
How do we calculate specificity
True negatives/ true negatives + false positives
How do we calculate sensitivity
true positives/ true positives + false negatives
Define validity
a measure of how well a test distinguishes diseased from non-diseased individuals. The concept can be equally well applied to symptoms and signs. A completely valid test/symptom/sign will be positive for all cases and negative for all non-cases.
Define gold-standard
to determine validity it is necessary to have a gold standard that distinguishes diseased from non-diseased people. The idea of a gold standard suggests a degree of certainty that is rarely found. Uncertainty exists in distinguishing diseased from normal (see Is there anything wrong?, [link]), in the interpretation of test results and the defining of cut off points. However, the concept of validity is predicated on that of a true state that can be known.
What are the clinical uses of a predictive value
It is a measure of how likely the patient is to have (or not have) a condition given that they have had a positive (or negative) result.
When is the cervical test offered and how often
Every 3 years for women aged 25-49, every 5 years for women aged 50-64
When is the HPV vaccine given
girls aged 11 to 13 in Scotland
girls aged 12 to 13 in the rest of the UK.
