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Flashcards in Danny Liew Lectures Deck (94):
0

What is level one level of evidence?

systematic review of RCTs

1

What is PICOT?

Population
Intervention
Comparator/Control
Outcome
Timing

2

What do you call the extent to which the results of a study are valid for the sample studied?

internal validity

3

What does internal validity depend on? 3 things

study design
data collection
data analysis

4

Why randomize? 2 reasons

reduce confounders

5

Why would you stratify randomization? eg. country/smoking status

make composition of groups more similar with regarding key confounders and reduce confounding

6

what's selection bias?

investigators assigning to particular intervention

7

Why blind?

reduce information bias

8

Who's blinded?
1. single-blind
2. double blind
3. triple blind

1. subjects
2. subjects + investigators
3. subjects + investigators + outcome assessors

9

when outcomes are determined according to strict standardized, objective criteria, this is called:

Objective Outcome Ascertainment

10

How would you achieve Objective Outcome Ascertainment in a multi-centre study?

have a centralised process

11

What's intention to treat?

Keeping the subjects in their randomized group regardless of actual dropouts, crossovers, losses

12

What's the point of intention-to-treat?

reduce selection bias

13

What does ITT analysis do to treatment effect?

always underestimates because assumes:
less in intervention group
more in control group

14

What's the p-value?

probability that the result arose from chance

15

What's the cut off for p-value?

0.05 not stat significant

16

What's a 95% confidence interval?

interval where you're 95% sure the value is within

17

What's it mean if there's no null value?

the result is stat significant

18

What is a null value?

if there's no difference between groups compared:
1.0 for ratios
0 for absolute risk differences

19

How are precision and Confidence Interval (CI) related?

The narrower the CI window, the more precise

20

If you have bigger sample size vs. smaller sample size, how does that affect CI width?

bigger = narrower CI
smaller - wider CI

21

What is a type 1 alpha error?

study shows effect, but in reality no effect

22

what is a type 2 beta error?

study shows no effect, reality there is an effect. (false negative)

23

What would lack of power indicate?

non stat significant results possibly due to small sample size

24

Number needed to treat is what?

how many people need to be treated to prevent outcome in one person

25

how to calculate NTT?

1 / absolute risk or rate reduction

26

What's NNT affected by? 2 things:

relative effect
underlying likelihood of outcome

28

External validity depends on?

PICOT

29

Does a systematic review only focus on a single question?

Yes.

30

How is the criteria for the systematic review?

well-defined

31

what kind of data does a systematic review looks at?

clinical trial
observational data

32

4 key words for systematic review process:

identifies
appraises
selects
synthesises

33

What are the 4 purposes of a meta-analysis?

increase power
resolve uncertainty
improve precision
answer other questions

34

3 important data sources for systematic review

Medline, Embase, CINAHL etc
reference list
grey literature

35

inclusion/exclusion criteria?

inline with question
PICOT
sample size
aware of bias eg. language

36

How many people for selecting studies?

2 people independently

37

Quality of studies included important why?

garbage in = garbage out

38

EXAM question re: forest plots: make sure you know it!

Got it?

39

what should be done about heterogeneity?

minimized

40

what determines weighting of ind. studies?

sample size

41

2 measures of outcome important in systematic review?

relative: RR, OR
absolute: mean difference

42

validity of a meta-analysis relies on what?

studies that are similar enough to be pooled

43

What two kinds of similarity determines metaanalysis potential?

statistical - effect sizes/variances
non-statistical - PICOT

44

Can you objectively assess non-statistical heterogeneity?

nope.

45

When do you order a diagnostic test?

if clinical suspicion of disease

46

Are the results mostly definitive or preliminary in a diagnostic test?

Mostly definitive

47

Whats the purpose of a diagnostic test?

to confirm disease

48

Who do you apply a screening test to?

no clinical suspicion of disease

49

Are the results mostly definitive or preliminary in a screening test?

preliminary - need confirmation

50

How do you calculate sensitivity?

True Pos/True Pos+False Neg
% positive test who actually have it

51

How do you calculate Specificity?

True Neg/True Neg+False Pos
% negative test who actually don't have it

52

How do you calculate Positive predictive value?

TP/TP+FP
% positive tests that are truly positive

53

How do you calculate Negative predictive value?

TN/TN+FN
% negative tests that are truly positive

54

Are sensitivity and specificity constant?

Yes, they are inherent to a test

55

What are PPV and NPV dependent on? 2 things:

Sensitivity+Specficity
Prevalance of disease

56

Utility of diagnositc/screeing test is highly dependent on what?

prevalence of disease

57

Should you just screen EVERYONE?

need to be targeted to high risk groups: prostate exam to men over 50

58

T/F? To screen a disease you should use a diagnostic test?

False

59

FEV1 and COPD uses a continuous scale, what denotes disease versus non-disease?

arbitrary thresholds

60

If you have a lower threshold, how does that affect sensitivity/specificity?

increased sensitivity
decreased sensitivity

61

If you have a higher threshold, how does that affect sensitivity/specificity?

decreased sensitivity
increased sensitivity

62

What is a Receiver Operator Characteristic curve (ROC)?

plot of 1-specificity vs. sensitivity
represents trade-off between sensitivity/specificity.

63

Ideal test on an ROC curve is where?

upper left, 100% sensitivity with 0% 1-specificity

64

What is a worthless test on ROC curve?

diagnonal line, with a perfect correlation of axis, that means 50-50 chance it's there or not there.

65

on an ROC curve, where do you find the discriminating ability of a test?

area under the curve, above the diagonal

66

What is the rationale for screening?

early detection -->better outcomes

67

what is primary prevention?

identifying risk factors

68

what is secondary prevention?

identifying early disease

69

what population is screening undertaken on?

largely healthy people

70

What is an important criteria for screening that may be overlooked?

cost-benefit analysis

71

limitations of screening tests include 4 things:

inaccuracy
not cost-effective
physical/psych side-effects
biases

72

3 biases in screening

selection
lead-time
length-time

73

What is selection bias in screening?

healthy people more likely to be screened

74

What is lead-time bias in screening?

early detection, not prolonged survival

75

What is length-time bias in screening?

detection of non-aggressive diseases

76

Whats the difference between prevalence and incidence?

Prevalence: number of existing cases at a single point in time (% or proportion)
Incidence, is number of new cases in a time interval (rate)

77

Risk=n/P expand:

new cases/population at risk

78

Rate=n/tx expand:

new cases/follow-up person-time

79

What's so great about person-time?

reflects a more accurate picture of the rate

80

T/F Risk is better than rate in representation?

Nope. Rate is better cause it uses person-years

81

What's the difference between risk and hazard?

Risk is a single point in time
Hazard: continuously updated rate, applicable throughout the entire time period

82

2 kinds of associations are:

Cause - effect
correlation

83

Difference between Absolute risk/rate and relative risk?

Absolute: isolated number, no indication of causes
Relative risk: provides association

84

T/F? Relative Risk, risk ratio mean the same thing?

True

85

How do you calculete RR?

Re/Ru
Risk/rate exposed
risk/rate unexposed

86

What is attributable risk?

absolute magnatude of change in risk/rate of outcome with associated exposure (exam)

87

How to calculate AR?

Re-Ru (exam)

88

How to calculate AR %?

Re-Ru/Re x100

89

What does AR% mean?

proportion of incident disease among exposed people that is DUE TO exposure

90

How to calculate Population Attributable risk? (PAR?)

PAR = Rt-Ru
Rt-risk/rate in whole population
Ru-risk/rate in unexposed

91

How to calculate PAR%?

Rt-Ru/Rt x100

92

Preventable fraction is a synonym for what?

Population attributable risk percentage

93

What does preventable fraction mean?

If you remove the risk factor, you help the PAR% number of people

94

Can a study be externally valid if it's not internally valid?

NOPE.