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PHAR 271 > EBM Midterm > Flashcards

EBM Midterm Flashcards

1
Q

What is internal validity

A

Are the results due to the intervention/exposure that was studied or something else

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2
Q

What are the major threats to internal validity

A

Chance, Bias, confounding

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3
Q

What is chance

A

random error in measurements

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4
Q

What is confounding

A

confusion of effects

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5
Q

bias

A

Problems with the way a study was designed, conducted or analyzed that leads to incorrect results or conclusions

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6
Q

what is external validity

A

Are the results applicable (generalizable) to other populations (patients), settings and time

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7
Q

what is the P value

A

The probability the results are due to chance rather than a real treatment effect

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8
Q

Do you want a small p-value or a large p-value

A

Want it to be less than 0.05

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9
Q

How do you deal with chance

A

Increase sample size

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10
Q

Does statistical significance always mean clinical significance

A

NO

BUT can’t have something be clinically significant if it isn’t statistically significant

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11
Q

What does PICO stand for/

A 
The question of the study 
P: population/patient
I: intervention/exposure
C: comparison (control/other intervention)
O: outcome (result of the intervention)
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12
Q

What are the three things integrated in EBM?

A

evidence
clinical expertise
patient values

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13
Q

How do you deal with confounding

A

RANDOMIZATION

ensures group are similar in all aspects (known and unknown)

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14
Q

Where do we look in a study to see if our control and intervention groups are similar in baseline characteristics

A

TABLE 1

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15
Q

What are other ways confounding can be mitigated other than by randomization?

A

Stratification: try and make sure there are similar numbers in each group
Matching: matched on known factors
Multivariable models: logistic regression

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16
Q

What is selection bias

A

Systematic error (or differences) in how the study subjects were selected or who participated

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17
Q

Does selection bias effect internal or external validity

A

External validity

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18
Q

what are examples of selection bias

A

Volunteer bias: People who volunteer/participate in studies are different from those who don’t
Adherer bias: employed individuals adhere to medications better
Attrition bias: lost to follow up

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19
Q

What is information bias

A

Problems with measuring, collecting or classifying information (exposure and/or outcomes)

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20
Q

what are some examples of information bias

A

Outcome errors: problems with measuring tools and the actual measurements
Recall bias: individuals remember things differently (ie. pain scale)
Interviewer bias: Interviewer asks about exposure/outcome differently
Detection bias: If you look you will find it

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21
Q

How do you minimize bias

A

BLINDING

WILL NEVER TOTALLY ELIMINATE IT!

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22
Q

What is publication bias

A

Authors and journals tend to publish positive findings (especially drug trials)

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23
Q

What is an RCT

A

Tests whether an intervention works by comparing it to a control condition
Subjects have equal chance of being assigned to each group

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24
Q

What is a parallel RCT design

A

Regular: how you think an RCT works

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25
Q

What is a cluster randomized RCT

A

Clusters of individuals are randomized instead of individuals
Used in hospitals/pharmacies

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26
Q

what is a cross-over RCT?

A

The patient becomes their own control because they take turns in the control and intervention group.
Takes more time because need a wash-out period for the drugs.

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27
Q

What does a power calculation help us determine?

A

The study sample size needed to show if a difference exists

MUST be determined before the study starts

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28
Q

What is unique about the inclusion/exclusion criteria in RCTs

A

VERY STRICT

limits generalizability

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29
Q

What must be included in intervention criteria?

A

Drug (dose, regimen, delivery method, follow-ups, length of intervention)
Procedure (What’s involved, timing, follow-up, length of intervention)

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30
Q

What is an objective outcome

A

Measurable (blood pressure, lipid levels)

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31
Q

what is a subjective outcome

A

Subjects interpretation (back pain)

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32
Q

what is a hard endpoint

A

Death, stroke, MI

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33
Q

what is a surrogate endpoint

A

Blood pressure (which can lead to stroke)

34
Q

What is a primary endpoint

A

Main result that is measures at the end of the study to see the effect of the intervention

35
Q

What is a secondary endpoint

A

Additional results of interest but not main focus
Caution when interpreting as the study wasn’t designed around them (Power calculation is based on the primary endpoint)
NEVER make a decision based solely on a secondary endpoint

36
Q

What is a composite endpoint

A

A primary endpoint that contains several events (Instead of just looking at death as a primary outcome, you include MI, stroke, and death)

37
Q

What is the difference between an outcome and the results

A

Outcome is the thing we want to measure, results are the statistical analysis of the measurements

38
Q

what are the 3 methods of randomization

A

Complete: regular randomization (ie. flipping a coin)
Block: block of 6 randomized, 3 in intervention, 3 in control
Stratified: trying to achieve similarities in baseline characteristics

39
Q

What is Intention to Treat

A

Analyzing the data for ALL patients and according to the group they were originally randomized to
ONCE RADOMIZED ANALYZE

40
Q

How do you know if ITT to treat was done

A

look at the results table and the population that was analyzed

41
Q

what is the importance of ITT?

A

preserves the value of randomization

keeps important data that could otherwise be lost

42
Q

what is per-protocol

A

analyzing data only from subjects who completes the study or followed protocol exactly

43
Q

what is the placebo effect

A

Perceived or actual effect from an ineffectual or inactive treatment

44
Q

what are observational studies

A

Observe the effect of an exposure or intervention) on an outcome without interfering with anything

45
Q

what are the advantages of observational studies

A

more practical/feasible
more ethical: not denying treatment
real-world: larger inclusion criteria (pregnant, elderly, and kids); real-life situations (comorbidities, non-adherence)

46
Q

Disadvantages of observational studies

A

Confounding
Bias
Chance (not an issue as there is a larger population)

47
Q

What is a case report

A

Describes and interprets an individual case

48
Q

advantages of case reports

A

Useful in identifying new or unusual trends or diseases
Useful in identifying new drug effects (good or bad)
Describe novel interventions (Treatment, Diagnostic procedure)
Suggest areas for further research or alarm

49
Q

what are disadvantages of case reports

A

Difficult to interpret

can’t confirm or prove anything: one time story

50
Q

what is a case series

A

Collection of individual reports which typically occur within a fairly short period of time

51
Q

what is a cross-sectional study

A

Looks at population or study sample at one point in time

USEFUL FOR DESCRIBING PREVALENCE

52
Q

advantages of cross-sectional studies

A

good for determining prevalence
Useful for quick examination of potential associations
inexpensive

53
Q

disadvantages of cross-sectional studies

A

CANT determine incidence: how many new cases

54
Q

what is a case-control study

A

retrospective
Compare the proportion of cases (have already had the outcome) with the exposure to the proportion of controls (no outcome) with the exposure

55
Q

advantages of case-control studies

A

good for studying rare diseases or outcomes
quick to do as the outcome has already occurred
good for establishing association

56
Q

disadvantages of case-control

A

not randomized
susceptible to bias
only suggest associations: cannot prove cause and effect

57
Q

what is a cohort study

A

Groups (or cohorts) of subjects are created and compared according to exposure
Exposed vs. unexposed group
Groups followed over time to see if outcome occurs
BEST type of observational study for finding a valid association

58
Q

what is a prospective cohort study

A

At the start of the study, outcome hasn’t occurred yet

59
Q

what is a retrospective cohort study

A

Outcome occurred before the study started

60
Q

advantages of prosepctive studies

A

conducted in real time
have some control over what data you want to collect and where it is coming from
can manage some confounders

61
Q

advantages of retrospective studies

A

good for long follow-up studies

HOWEVER HAS DATA LIMITATIONS

62
Q

what is the most important thing to consider when choosing participants for a cohort study

A

MUST EXCLUDE DATA FROM PEOPLE WHO HAD THE OUTCOME BEFORE THE EXPOSURE (ex. had an MI and then was put on BP medication)

63
Q

advantages of cohort studies

A

Provides highest level of evidence for observational studies
Can study multiple outcomes after a single exposure
Can find relative risk

64
Q

disadvantages of cohort studies

A

Susceptible to bias
Not randomized so susceptible to confounding
More resource intensive than other observational studies

65
Q

what kind of results can be given from studies (2)

A

mean (or mean change)

Proportion (fraction of the total that possesses the outcome)

66
Q

Can you use odds ratios and risk ratios with mean results

A

NO only proportions

67
Q

what is the ARD/ARR

A

absolute risk reduction
absolute risk difference
The absolute difference between the probability of the event in the control group and probability of the event in the intervention group

68
Q

what is the relative risk

A

Shows that the risk of an outcome in the intervention group is compared to the risk in the control group
Probability of event (intervention group)/probability of event (control group)

69
Q

what is the threshold for seeing a difference when using mean results?

A

0 (also for CI to be statistically significant cant cross 0)

70
Q

What does a relative risk or odds ratio=1 mean

A

NO difference in odds/risk between the groups

71
Q

What does a relative risk or odds ratio>1 mean

A

HIGHER risk/odds of outcome in intervention group

72
Q

What does a relative risk or odds ratio<1 mean

A

LESS risk/odds of outcome in intervention group

73
Q

what is an odds ratio (OR)

A

Shows the odds of the outcome occurring in the intervention group compared to the control group

74
Q

what is relative risk reduction or increase

A

RRR=1-RR

75
Q

what is NNT

A

Number of subjects who would have to be treated (receive the intervention) in order for one additional subject to “benefit” in comparison to control

76
Q

what is NNH

A

Number of patients who would be treated before you see one additional subject with an adverse event compared to control

77
Q

what does CI show us

A

can show us the magnitude of effect
can show us if there really is a difference (statistical significance)
If the CI crosses the “no difference” threshold then there is not a difference
For MEANS or PROPORTIONS: no difference=0
For RELATIVE RISK or ODDS RATIO: no difference=1

78
Q

what is a non-inferiority trial

A

Clinical trial to establish that an intervention is not clinically worse than a comparison by more than a pre-determined margin

79
Q

what is the non-inferiority margin

A

Used to determine the sample size needed for adequate power

80
Q

what is a propensity score

A

The probability that a subject would be in a particular treatment (study) group based on their observed baseline characteristics

81
Q

what do propensity scores help with

A

Helps reduce selection bias and confounding in observational studies
DOESN’T replace the value of randomization

PHAR 271 (1 decks)

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