Eqns

Question 1

What is sensitivity?

Answer 1

The proportion of all people with disease who test positive or the probability that the test is positive when dz is present

Question 2

Sensitivity=

Answer 2

TP/(TP + FN)

Question 3

When do you want high sensitivity?

Answer 3

Screening purposes–

Catch ‘em all (pokemon players are very sensitive)

Question 4

What is specificity?

Answer 4

Proportion of all people without dz who test negative or probability that the dz is absent when test is negative

Question 5

Specificity=

Answer 5

TN/(TN+FP)

Question 6

When do you want high specificity?

Answer 6

To confirm a screening test

Question 7

PPV

Answer 7

Positive predictor value- proportion of positive test results that are true positive
PPV= TP/(TP+FP)

Question 8

NPV

Answer 8

Negative predictor value- proportion of negative test results that are true negative
NPV= TN/(TN+FN)

Question 9

How do PPV and NPV vary?

Answer 9

They vary with prevalence or pretest probability

PPV- high pretest probability–high PPV
NPV - high pretest probability – low NPV

Question 10

Incidence:

Answer 10

number of new cases / number of people at risk

During specific time period

Question 11

Prevalence:

Answer 11

number of existing cases/ number of ppl in population

At a point in time

Question 12

Odds ratio:

Answer 12

(True positive * True Negative)/ (False Positive * False Negative)

Question 13

Relative risk:

Answer 13

(a/(a +b)) / (c/(c+d))

Question 14

Attributable Risk:

Answer 14

(a/(a +b)) - (c/(c+d))

Question 15

Relative Risk Reduction

Answer 15

1- relative risk (RR)

Question 16

Absolute risk reduction:

Answer 16

(c/(c+d)) - (a/(a +b))

Question 17

NNT (number needed to treat)

Answer 17

1/ARR (absolute risk reduction)

Question 18

NNH (number needed to harm)

Answer 18

1/AR