Screening: statistics

Question 1

disease present and positive test

Answer 1

true positive

Question 2

disease present and negative test

Answer 2

false positive

Question 3

disease absent and negative test

Answer 3

true negative

Question 4

disease absent and positive test

Answer 4

false negative

Question 5

SENSITIVity

Answer 5

probability of disease present and positive test (true positive) / disease present

Question 6

SPECIFICity

Answer 6

probability of disease absent and negative test (true negative) / disease absent

Question 7

describe relation of sensitivity and specificity to prevalence

Answer 7

sensitivity is looking at DISEASED only
specificity is looking at HEALTHY only
–> no overlap

furthermore the test will give the same proportion within diseased/healthy groups, regardless of their size

Question 8

positive predictive value

Answer 8

probability of disease present and positive test (true positive) / positive test

Question 9

negative predictive value

Answer 9

probability of disease absent and negative test (true negative) / negative test

Question 10

describe relation of PPV and NPV to prevalence

Answer 10

within each, both diseased and healthy individuals are looked at.

therefore, change in prevalence will result in change to proportions and therefore PPV and NPV