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BMS I > EBM Day 4 > Flashcards

EBM Day 4 Flashcards

1
Q

Variance

A

Average of squared differences from the mean

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2
Q

SD

A

square root variance

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3
Q

SE +meaning

A

SD/sqrtN

The SD of the distribution of mean value

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4
Q

Central Limit Therom

A

When normal diet

More samples you take, more closer you get true mean

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5
Q

CI calc + meaning

A

mean+/-Z(usually 1.96)*SE

this is where we think sample mean lies

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6
Q

Point estimate

A

estimate of some value derived from study (mean, regression coeff etc)

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7
Q

Z=+1.96
Z=-1.96
what %

A

both in 97.5% or 2.5% chance of not being in

total = 5%

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8
Q

When to compare CI to 0 (2)or 1 (3)

A

0=correlation or dif
1-hazard ratio, relative risk, odds ratio (these all kinda same thing too)
ESSENTIALLY WHAT THE NULL IS

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9
Q

Smaller CI

A

Higher precision and more n

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10
Q

Marginally sig

A

A little bias either way can make sig or not sig

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11
Q

2x2 false pos and negative chart

A

draw

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12
Q

Misclassifcation

A

False positives and false negatives

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13
Q

TN, FN, TP, FP chart and sensitivity

A

draw

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14
Q

+PV and -PV and meaning

A

Predictive value

TP/TP+FP
TN/FN+TN

Probability that a patient with positive test result truly has disease

Probably that a patient with negative result does not have disease

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15
Q

Sensitivity and meaning and when best

A

TP/TP+FN

No false negatives
Negative result=rule out
SNOUT
Sennstive, negative rules out disease

GOOD FOR cheap and initial procedures

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16
Q

Specificity and meaning and when best

A

tN/FP+TN

No false positives
Positives-rule in
SPIN
Specific, positive rules in

GOOD FOR EXPENSIVE and dangerous PROCEDURES

17
Q

Draw cut off point table with TP, TN, FP, FN

A

draw

18
Q

Prevalence

A

TP+FN/TOTAL

19
Q

LR+ and meaning

A

Likelihood ratio

TP/TP+FN/
FP/FP+TN

how likely to have disease when test is positive

how many times more likely a (+) test result is to be found in people with disease compared to those without

20
Q

LR- and meaning

A

FN/TP+FN/
TN/TN+FP

how likely to have disease when test is negative

how many times more likely a (-) test result is to be found in people with disease compared to those without? i think

21
Q

TP=
FP=
FN=
TN=

A

SE
1-SP (false positive rate)
1-SE
SP

22
Q

1-SP

SEN

A

false postive rate

True positive rate

23
Q

ROC Curve

A

Senstivity (TP) on Y
1-Specifity (FP rate) on X

Upper left is where you wanna be

24
Q

Relationship between predictive value and prevalence

A

Lower prevalence, lower predictive value

25
Q

Post test probability

A

Probability of a disease after test result is known

26
Q

Natural Frequencies Approach

A

Choose large population
Use sensitivity to find TP
Use 1-spec to find FP
TP/TP+FP=+PV

27
Q

Increase pretest probability

A

consider demograpics, presentation, clinical setting

28
Q

Nomogram

A

use Pretest prob (prevalance) and then find LR and draw line to Post test prob (PV)

29
Q 
LR to change in disease prob %
10
5
2
.5
.1
A 
45%
30%
15%
-30%
-45%
30
Q

Parallel testing and sens/spec relationship

A

Test A or B, or C positive makes all positive

Sens up, spec down

31
Q

Serial testing and sens/spec relationship

A

Test A AND B AND C postiv

Send down, Spec up

32
Q

Independent tests

as related to serial/parallel testing

A

Assumed by parallel and serial testing

33
Q

Index Test vs reference

A

new test when compared to gold standard

34
Q

Basic approach to evaluating diagnostic tests

A 
select patients
test all patients with index
diagnose in series then do gold standard
Compare results of index test to reference index results
Look for sources of error
35
Q

5 challenges to establishing accuracy in diagnostic test

A 
inappropraite ref standard
spectrum bias
verification bias
observor bias
chance
36
Q

Spectrum bias and big problem

A

including only highly selected patients (such as those who would benefit)

  - problem of including people who would benefit a lot, and very little and leaving out middle (where there would be a lot of false positives and false negatives
  - big change to specificity and sensitivity
37
Q

verification bias

A

work up bias

not giving both tests
reference may be too invasive to give if respond to index

38
Q

Observor bias (5 reasons why occur)

A

Ref standard is subjective
Index and reference standard not evaluated independently
Evaluators not blinded to results of other test

Evaluators not blidned to patient characteristics

39
Q

Must design index test without out this value

A

Reference standard-leads to bias if don’t do this

BMS I (30 decks)

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