Week 9 Flashcards
mass screening
whole population or subset
multiple or multiphasic screening
many screening tests at the same time
targeted screening
groups with a particular exposure
case-finding/ opportunistic screening
tested while at the doctors for another purpose
3 ways to distinguish between normal and abnormal
- normal as common
- abnormal associated with disease
- abnormal as treatable
- normal as common
Values that occur frequently are normal
Values that occur infrequently are abnormal
Normal distribution: 2.5% abnormal using + 2SD cut off
Percentile (95%): 95% normal and 5% abnormal
- abnormal associated with disease
Use of the distribution of measurements for both healthy/diseased people with an attempt to define the cut-off that separates the two groups
Results in some healthy people on the ‘abnormal’ side and some diseased people on the ‘normal’ side
- Abnormal as treatable
Definition of abnormal changes over time based on changing treatment thresholds
before screening, disease must be
Relatively common (prevalent) disease
Several consequences
Early treatment produces better outcomes
Considered a problem by people
Natural history well-understood
Relatively long preclinical phase when disease could be detected by screening
the screening test should be
Good accuracy OR high sensitivity and/or specificity Safe simple/logistically manageable Relatively cheap Acceptable to ‘healthy’ people
positive results threshold- screening test
tend towards high sensitivity not to miss potential disease
positive results threshold- diagnostic test
tend towards high specificity (true negatives)
more weight given to accuracy and precision than to patient acceptability
positive result- screening test
indicates suspicion of disease (often used in combination with other risk factors) that warrants confirmation (diagnosis)
positive result- diagnostic test
result provides a definite diagnosis
in tests, we are most concerned about
false negatives
