Evidence based medicine

Question 1

3 contexts in which diagnoses sought

Answer 1

1. screening
2. case finding
3. people come in with prob

Question 2

what is test for PE

Answer 2

D-dimer test - product of breakdown clot

Question 3

interpretation of D-dimer

Answer 3

500 pos. for thrombosis

Question 4

what is type 1 error

Answer 4

false +ve

• abnormal person
• has another disease

Question 5

what is type 2 error

Answer 5

false -ve

• person’s disease give normal value
• tech problem with test

Question 6

def. sensitivity

Answer 6

TP/TP+FN

Question 7

def. spec.

Answer 7

TN/TN+FP

Question 8

what do we want to rule out

Answer 8

highly sensitive test (few false neg) (SnOut)

Question 9

what do we want to rule in

Answer 9

highly specific test (few false pos) (SpIn)

Question 10

what is trade off

Answer 10

as move cutoff value, you trade spec. for sens.

Question 11

what is ROC curve

Answer 11

refers to the tradeoff in sens and spec when moving values

Question 12

what is test vs. gold standard

Answer 12

test gives you an indication of when you should do the gold standard

Question 13

what steps in predictive values

Answer 13

1. start with Pt that has a pretest probability
2. administer the test
3. given results, now how likely to have disease

Question 14

where does pre-test probability come from (4)

Answer 14

1. experience (gut)
2. pop. prevalence
3. published data on patients with similar issues
4. clinical prediction rules

Question 15

what are clinical prediction rules

Answer 15

decision making rules containing variables from Hx, physcial and/or simple diagnostic tests

Question 16

what is pos. predictive value

Answer 16

TP/(TP+FP)

Question 17

what is neg. predictive value

Answer 17

TN/(TN+FN)

Question 18

what is prob. of disease if test is negative

Answer 18

100-NPV

Question 19

how does pre-test probability influence the test

Answer 19

even with same sens. and spec. , a low pre-test prob will mean a lower-posttest probability

Question 20

how to determine where to put the treatment threshold for post-test probability

Answer 20

based on out comes

Question 21

when to make threshold low (2)

Answer 21

1. disease serious if untreated

2. treatment is effective and inexpensive

Question 22

when to make threshold high

Answer 22

treatment risky or expensive

Question 23

def. likelihood ratio

Answer 23

prob. of that result in person who has disease/prob of that result in person who doesn’t have that disease

Question 24

what is LR used for

Answer 24

to effectively calculate post-test prob. of disease at multiple levels of a test

Question 25

formula for LR pos. test

Answer 25

sens/(1-spec)

Question 26

formula for LR neg. test

Answer 26

(1-sens.)/spec

Question 27

4 adv. of using LR

Answer 27

1. easy to determine post-test prob. using a nomogram
2. can use at multiple levels of test
3. with sequential tests can multiply LRs
4. at a glance can see how helpful findings might be

Question 28

2 LR magnitudes that are helpful

Answer 28

1. LR > 5-10 - helps for ruling disease in

2 LR