Diagnostic Tests and Screening Flashcards
What is validity?
Truth of result
Lack of bias
What is reliability?
Consistency of results, repeatability and reproducibility
How to improve reliability?
Repeat measurements improve reliability
Take several readings
Duplicate readings
What is sensitivity and specificity?
Sensitivity - If someone has a disease what is the probability that the test result will be positive
Specificity - if someone does not have the disease, what is the probability the test result will be negative
Primary and secondary intervention?
Primary is when the patient is healthy
Secondary is done around disease onset and signs or symptoms
What are the 5 criteria for screening a disease?
Criterion 1 - the condition is important in terms of frequency and impact
C2 - primary prevention is not effective or feasible
C3 - there is an identifiable pre-clinical stage of disease
C4 - there is a test that separates those with high probability of disease with those that have low probability
C5 - effective treatment is available and the outcome of early treatment is better than later treatment after clinical diagnosis
What are the main characteristics of a screening test?
Simple Safe Precise Have been validated Clear distinction of results Reasonable cost
What is lead time and length bias?
Lead time bias - Interval between the diagnosis of a disease at screening and the usual time of diagnosis
Length bias - slow growing diseases more often detected through screening
What are the 4 bias’s with screening?
Lead time
Length based sampling
Selection bias
Overdiagnosis bias
What are the advantages of screening?
Improved prognosis for true positives
Less radical treatment required
Reassurance for those with a true negative test result
Disadvantages of screening?
Longer period of awareness for true positives
Over treatment
False reassurance if false negatives
