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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
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.

Jason's Respiratory Block (20 decks)

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