4 - Therapys + RCTs Flashcards
1
Q
what is the most important consideration in the design of any experiment?
A
- to minimize error
2
Q
explain the association of power and error
A
- power = ability to statistically detect a diff btw groups when one exists (signal)
- error = unexpected variability within the outcome (noise)
- therefore finding a S.S. diff btw groups = signal/noise!
- little we can do about signal, much can be done about noise reduction!
3
Q
what is total error made up of?
A
- systematic and random error
4
Q
define systematic vs random error - how can it be prevented?
A
- systematic = bias, variability in the outcome that can be prevented or explained (threatens validity)
- random: variability in the outcome that cannot be explained (threatens precision and external validity)
- there will always be some amount of error
- prevented through design or removal during analysis
5
Q
how can we increase power? (3)
A
- decrease noise
- increase signal
- lower standards (increase willingness to accept t1 error)
6
Q
describe the conventional design of an RCT
A
- p 52
7
Q
describe importance of control groups and 2 types of control groups
A
- important for controlling threats to internal validity (whether change happened due to chance or it would have happened anyways?)
- no-treatment control and standard-of-care control
8
Q
what is the standard of care control group
A
- provides all medical treatment to all participants
- less statistically powerful (delta is smaller)
- may be more ecologically valid
- can’t compare with placebo if another valid standard of care exists (ethics)
9
Q
what is the no treatment control group
A
- may be limited to treatments with wait lists
- more statistically powerful than standard of care control group (delta is bigger)
- bigger signal, increased power, decreased n-size requirements
10
Q
name some features that limit bias in a design
A
balance of prognostic factors
- randomization
- allocation concealment
- blinding
- standardization of protocol
- intent-to-treat analysis
- completeness of follow-up
11
Q
describe the balance of prognostic factors
A
- prognostic means controlling for what you can up front or at the end through analytical methods
- look to make sure in the table (should be provided by researcher) that important characteristics are similar btw 2 groups
- note that there is no point in adding p values for comparing (redundant and use up our alpha)
- p 53
12
Q
what are the 4 types of randomization?
A
- simple
- stratified
- blocked
- minimization
13
Q
what is stratified randomization?
A
- separating samples into several subsamples to balance prognostic factors btw groups
- ie males and females - each group separated equally among tx and ct
- good for smaller studies
14
Q
what is blocked randomization?
A
- controls allocation of participants so there is an equal distribution of participants btw groups
- blocks are multiples of the number of groups you have (ie if you have 3 groups, block size can be 3, 6, or 9)
- good for smaller studies
15
Q
what is minimization randomization?
A
- calculated imbalance within each prognostic factor should the patient be allocated to a particular treatment group. various imbalances added together to get overall study imbalance. patient is assigned to treatment group that would minimize the imbalance.
- uses computer algorithm
16
Q
what is allocation concealment?
A
- person making decision about patient eligibility is unaware of which group they are assigned to until decision about eligibility has been made
- internal validity error!
17
Q
what is selection bias?
A
- systematic errors in the measurement of the effect of treatment due to differences btw those who are selected and those who are not
- internal validity error!
