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CHAPTER 5: Assesing the Validity and Reliability of Diagnostic and…
CHAPTER 5: Assesing the Validity and Reliability of Diagnostic and Screening Tests
Component of Validity
Sensitivity
ability of the test to identify correctly those who have disease
Specificity
ability of the test to identify correctly those who do not have disease
Test Result
Negative
False Negative
Have disease but test negative
indeed critical
True Negative
Do not have the disease and test negative
Positive
False Positif
Do not have the disease but test positive
burden on the health care system
True Positif
Have the disease and test positive
Continues Variable
choice of cutoff level relates to the relative importance of false negativity for the disease in question
Predictive Value of a test
what proportion of patient actually have the disease
positive predictive value (PPV)
number of true positive /( true positive + false positive)
is affected by two factors
prevalence of the disease in the population tested
the specificity of the test being use
relationship with specificity of the test
negative predictive value (NPV)
the probability that this patient does not have the diseasse
relationship between positive predictive value and disease prevalence
the highger the the prevalace the higher the predictive value
most productive and efficient if it is directed to a high-risk target population
result pf any test must be interpreted in the context of the prevalence of the disease in the population from which the subject originate
Use multiple Tests
Sequential ( Two Stage) Testing
Net Specificity
net gain
Net Sensitivity
net loss
Definition: 1 test for rapid test, 2 test to confirm (PCR) high sensitivity
Simultaneous Testing
loss spesificity
Reliability (repetability) of the test
factor
intrasubject variation
intraobserver variation
interobserver variation