Screening Flashcards
Why is screening classed as a cyclical process?
People who have a negative test result or who are found not to have the disease are screened again at a later date to check whether they develop the disease at a later date
What is the definition of a true negative?
Absent disease + negative test result
Absent disease + positive test result = ?
False positive
Present disease + negative test result = ?
False negative
What is a true positive?
Disease present + Positive test result
How is sensitivity calculated?
True positive / (True positive + False negative)
How is specificity calculated?
True negative / (False positive + true negative)
True positive / (True positive + false positive) = ?
Positive predictive value
True negative / (False negative + True negative)
Negative predictive value
‘The proportion of people with the disease who are identified as having it by a positive test result’
Sensitivity
The proportion of people without the disease that are reassured by a negative test result
Specificity
What is the positive predictive value?
The probability that a person with a positive test result actually has the disease
What is the negative predictive value?
The probability that a person with a negative test result does not actually have the disease
What are the characteristics of high sensitivity testing?
Maximises identification of disease
Low false negatives
High false positives
What are the characteristics of high specificity testing?
Detect only people with the disease
Low false positives
High false negatives
What is the lead time basis?
a new factor when comparing, in detection of disease, a traditional test with a new or experimental test but the outcome of the disease is unchanged
When devising a new screening programme, what are some requirements of ‘the condition?’
Must be fully understood
Must have a latent or asymptomatic phase
Must be an important problem
Most have a detectable factor
When devising a test for a new screening programme, what are some requirements?
Simple, safe, precise and valid
Easily done
Suitable cut off level
Distribution should be known
When devising a treatment for a new screening programme, what are some requirements?
Treatment or intervention must be effective
Evidence that the outcome is better with treatment
Treatment should be appropriate
