RCR class #9 Flashcards
Def power
The abilty to correctly declare a treatment benefit (find an effect if it exists)
power equation
power = 1-B where B is the prob of a type II error (failure to reject the null when the alt is true
What power do we want in an RCT
80% to 90% these are important converntions
T/f power is the prob of finding a stat sig difference
of size delta
F, it is the probability of finding a difference between the two interventions
If a trial is underpowered it should…
not be done
Too high a power does what
too much he wasted resources and declared a tiny irrelevant effect.
Just right power
80-90%
trial 80% 90% is for what effect size
the minimum effect size that would be clinically signifcatn
Is it better to over or under estimate power
OVer is better , if we overestimate can always stop early for benefit.
Why are RCTs underpowered f? (2)
clinical benefit of a new intervention is oft lower than estimated.
- benefit of a new intervention found in an RCT is generally lower than in a population or clinic samples.
2. unaccounted for LTFup and cross over
effect size?
the minimal effect detected within a given sample size.
Key question about effect size?
What is the minimal effect size that would be clinically relevant.
Dichotomous/categorical outcome delta?
Difference in proportions between two arms
Cont outcome delta
difference in means in two arms/ SD
Time to event delta
HR reduction for control relative to experimental
