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Jason's Respiratory Block > Danny Liew Lectures > Flashcards

Danny Liew Lectures Flashcards

0
Q

What is PICOT?

A 
Population
Intervention
Comparator/Control
Outcome
Timing
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1
Q

What is level one level of evidence?

A

systematic review of RCTs

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2
Q

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

A

internal validity

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3
Q

What does internal validity depend on? 3 things

A

study design
data collection
data analysis

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4
Q

Why randomize? 2 reasons

A

reduce confounders

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5
Q

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

A

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

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6
Q

what’s selection bias?

A

investigators assigning to particular intervention

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7
Q

Why blind?

A

reduce information bias

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8
Q

Who’s blinded?

  1. single-blind
  2. double blind
  3. triple blind
A
  1. subjects
  2. subjects + investigators
  3. subjects + investigators + outcome assessors
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9
Q

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

A

Objective Outcome Ascertainment

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10
Q

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

A

have a centralised process

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11
Q

What’s intention to treat?

A

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

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12
Q

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

A

reduce selection bias

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13
Q

What does ITT analysis do to treatment effect?

A

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

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14
Q

What’s the p-value?

A

probability that the result arose from chance

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15
Q

What’s the cut off for p-value?

A

0.05 not stat significant

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16
Q

What’s a 95% confidence interval?

A

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

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17
Q

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

A

the result is stat significant

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18
Q

What is a null value?

A

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

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19
Q

How are precision and Confidence Interval (CI) related?

A

The narrower the CI window, the more precise

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20
Q

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

A

bigger = narrower CI

smaller - wider CI

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21
Q

What is a type 1 alpha error?

A

study shows effect, but in reality no effect

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22
Q

what is a type 2 beta error?

A

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

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23
Q

What would lack of power indicate?

A

non stat significant results possibly due to small sample size

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24
Q

Number needed to treat is what?

A

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

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25
Q

how to calculate NTT?

A

1 / absolute risk or rate reduction

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26
Q

What’s NNT affected by? 2 things:

A

relative effect

underlying likelihood of outcome

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28
Q

External validity depends on?

A

PICOT

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29
Q

Does a systematic review only focus on a single question?

A

Yes.

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30
Q

How is the criteria for the systematic review?

A

well-defined

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31
Q

what kind of data does a systematic review looks at?

A

clinical trial

observational data

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32
Q

4 key words for systematic review process:

A

identifies
appraises
selects
synthesises

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33
Q

What are the 4 purposes of a meta-analysis?

A

increase power
resolve uncertainty
improve precision
answer other questions

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34
Q

3 important data sources for systematic review

A

Medline, Embase, CINAHL etc
reference list
grey literature

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35
Q

inclusion/exclusion criteria?

A

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

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36
Q

How many people for selecting studies?

A

2 people independently

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37
Q

Quality of studies included important why?

A

garbage in = garbage out

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38
Q

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

A

Got it?

39
Q

what should be done about heterogeneity?

A

minimized

40
Q

what determines weighting of ind. studies?

A

sample size

41
Q

2 measures of outcome important in systematic review?

A

relative: RR, OR
absolute: mean difference

42
Q

validity of a meta-analysis relies on what?

A

studies that are similar enough to be pooled

43
Q

What two kinds of similarity determines metaanalysis potential?

A

statistical - effect sizes/variances

non-statistical - PICOT

44
Q

Can you objectively assess non-statistical heterogeneity?

A

nope.

45
Q

When do you order a diagnostic test?

A

if clinical suspicion of disease

46
Q

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

A

Mostly definitive

47
Q

Whats the purpose of a diagnostic test?

A

to confirm disease

48
Q

Who do you apply a screening test to?

A

no clinical suspicion of disease

49
Q

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

A

preliminary - need confirmation

50
Q

How do you calculate sensitivity?

A

True Pos/True Pos+False Neg

% positive test who actually have it

51
Q

How do you calculate Specificity?

A

True Neg/True Neg+False Pos

% negative test who actually don’t have it

52
Q

How do you calculate Positive predictive value?

A

TP/TP+FP

% positive tests that are truly positive

53
Q

How do you calculate Negative predictive value?

A

TN/TN+FN

% negative tests that are truly positive

54
Q

Are sensitivity and specificity constant?

A

Yes, they are inherent to a test

55
Q

What are PPV and NPV dependent on? 2 things:

A

Sensitivity+Specficity

Prevalance of disease

56
Q

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

A

prevalence of disease

57
Q

Should you just screen EVERYONE?

A

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

58
Q

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

A

False

59
Q

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

A

arbitrary thresholds

60
Q

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

A

increased sensitivity

decreased sensitivity

61
Q

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

A

decreased sensitivity

increased sensitivity

62
Q

What is a Receiver Operator Characteristic curve (ROC)?

A

plot of 1-specificity vs. sensitivity

represents trade-off between sensitivity/specificity.

63
Q

Ideal test on an ROC curve is where?

A

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

64
Q

What is a worthless test on ROC curve?

A

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

65
Q

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

A

area under the curve, above the diagonal

66
Q

What is the rationale for screening?

A

early detection –>better outcomes

67
Q

what is primary prevention?

A

identifying risk factors

68
Q

what is secondary prevention?

A

identifying early disease

69
Q

what population is screening undertaken on?

A

largely healthy people

70
Q

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

A

cost-benefit analysis

71
Q

limitations of screening tests include 4 things:

A

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

72
Q

3 biases in screening

A

selection
lead-time
length-time

73
Q

What is selection bias in screening?

A

healthy people more likely to be screened

74
Q

What is lead-time bias in screening?

A

early detection, not prolonged survival

75
Q

What is length-time bias in screening?

A

detection of non-aggressive diseases

76
Q

Whats the difference between prevalence and incidence?

A

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
Q

Risk=n/P expand:

A

new cases/population at risk

78
Q

Rate=n/tx expand:

A

new cases/follow-up person-time

79
Q

What’s so great about person-time?

A

reflects a more accurate picture of the rate

80
Q

T/F Risk is better than rate in representation?

A

Nope. Rate is better cause it uses person-years

81
Q

What’s the difference between risk and hazard?

A

Risk is a single point in time

Hazard: continuously updated rate, applicable throughout the entire time period

82
Q

2 kinds of associations are:

A

Cause - effect

correlation

83
Q

Difference between Absolute risk/rate and relative risk?

A

Absolute: isolated number, no indication of causes

Relative risk: provides association

84
Q

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

A

True

85
Q

How do you calculete RR?

A

Re/Ru
Risk/rate exposed
risk/rate unexposed

86
Q

What is attributable risk?

A

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

87
Q

How to calculate AR?

A

Re-Ru (exam)

88
Q

How to calculate AR %?

A

Re-Ru/Re x100

89
Q

What does AR% mean?

A

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

90
Q

How to calculate Population Attributable risk? (PAR?)

A

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

91
Q

How to calculate PAR%?

A

Rt-Ru/Rt x100

92
Q

Preventable fraction is a synonym for what?

A

Population attributable risk percentage

93
Q

What does preventable fraction mean?

A

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

94
Q

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

A

NOPE.

Jason's Respiratory Block (20 decks)

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