Screening Flashcards
Screening types
Population
Opportunistic
Pre-employment: occupational
Communicable- pandemic control
Wilson and Junger criteria
Important condition that if caught early w:
Sensitive and suitable test, can enable:
Effective treatment at:
Adequate and inexpensive facilities
Disadvantages of screening
Incorrect results
Adverse effects
Personal choice compromise
Advantages of screening
Early identification:
Cheaper treatment
Decreased suffering
Lead time bias
Earlier detection- seems like survival is prolonged
Length time bias
Disease with longer presentation duration more likely to be picked up by prevalence probability than more aggressive ones
Selection bias
Those who choose to participate may be different to those who don’t
Why is incidence rate used over incidence probability
Incidence probability ignores time to event and competing risks (eg death from other causes)
Incidence rate is an average
Hazard rate
Instantaneous rate of change
Incidence
Number of new cases in set time frame
Probability: of getting disease
Prevalence
Number of cases at single point in time
Probability: of having it.
Positive predicted values (PPV)
Proportion with positive result who have disease (correctly included)
Increases with high prevalence
True positives/ (true + false positives)
Negative predicted values (NPV)
Proportion with negative result who do not have disease (correctly excluded)
Decreased by high prevalence
True negatives / (true + false negatives)
Sensitivity
Probability of someone with disease having positive result (true positive)
True positives / (false negatives + true positives)
Specificity
Probability of someone without disease having negative results (true negative)
True negatives / (false positives + true negatives)
