US Physics: unit 8: QA statistics

why are 3 reasons statistics is needed

to look at the history of disease, advance knowledge, assess normal and the point it becomes a pathology

diagnostic test are used to confirm or exclude a

specific diagnosis

the certainty that a specific diagnosis can be confirmed or excluded determines _______of a study

usefulness

no test are ____ accurate

100 percent

how is statistics practiced in sonography

patients are classified as healthy or abnormal, instruments or test can be in perfect, and there are test error

what is a test error

when a patient is incorrectly classified

statistics offers a method to measure the ability of a specific test to give the ____ _____ for both health and ill patient

correct diagnosis

we must compare our lab test to a

gold standard

what is a gold standard

MRI, CT, arteriogram

what is the all important rule to sonography practice statistics

the gold standard is always right

this is when the lab test is positive at the GS is positive

true positive

this is where the lab test is positive but the GS is negative

false positive

this is where the lab lest is negative and the GS is negative

true negative

this is where the lab test is negative but the GS is positive

false negative

the ability to detect a disease when disease is really present, the degree to which it identifies all patients with disease

sensitivity

the ability to determine that there is no disease when the patient is truly normal, the degree to which it defines all patients without disease

specificity

tells use the percent of correct lab test compared to the gold standard, indicates the percent of patients in whom the test results are correct in identifying the presents or absence of disease

accuracy

incidence of disease in total population

prevalence

tells us the likelihood that the disease is really present, indicates the percent of patients with a positive test result who have the suspected disease

positive predictive value

- tells us the likelihood that disease is NOT present

- indicates the % of pts with a negative test result who do not have the suspected disease.

negative predicative value

what is the sensitivity formula

TP/(TP+FN)

what is the specificity formula

TN / (TN + FP)

what is the accuracy formula

TP+TN/(TN+TP+FN+FP)

what is the PPV formula

TP / (TP + FP)

what is the NPV formula

TN/(TN+FN)