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RegisterPower in the 2-stage design [Power / Sample Size]
Dear EM,
IMHO you are totally right in seeing the 80% power as an empirical parameter of the 2-stage evaluation which has no direct connection to the real power attained.
The Table I in Potvin et al. consistently show power empirical estimates (emphasis is for members of regulatory bodies
) between 70 to 80% if the CV is above 30% and sample size in stage 1 is low. Since the authors don't discuss this attained power <80% they seem to see this not as an issue and seem to accept power >70% as sufficient.
If you don't share this opinion you could of course adapt the 'power' in the sample size adaptation step to fit your needs.
Another possibility is the use of sample sizes based on 'expected' power which are usually higher than the ordinary ones. This should let to a power increase of the 2-stage evaluation.
❝ A background for my question is that I am fiddling a teenytiny bit with two-stage designs like those of Potvin et al. In the second step the target nominal power is 80% but due to the nature of the approach this figure is in some cases not achieved. Thus if we can define a realistic bsolute lower limit for power then we can tweak the method parameters so as to keep power above the magical or arbitrary threshold.
IMHO you are totally right in seeing the 80% power as an empirical parameter of the 2-stage evaluation which has no direct connection to the real power attained.
The Table I in Potvin et al. consistently show power empirical estimates (emphasis is for members of regulatory bodies
) between 70 to 80% if the CV is above 30% and sample size in stage 1 is low. Since the authors don't discuss this attained power <80% they seem to see this not as an issue and seem to accept power >70% as sufficient.If you don't share this opinion you could of course adapt the 'power' in the sample size adaptation step to fit your needs.
Another possibility is the use of sample sizes based on 'expected' power which are usually higher than the ordinary ones. This should let to a power increase of the 2-stage evaluation.
—
Regards,
Detlew
Regards,
Detlew
Complete thread:
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- ethics and power d_labes 2011-11-01 11:28
- ethics and power Ohlbe 2011-11-01 22:57
- ethics and power ElMaestro 2011-11-02 09:27
- ethics and power Ohlbe 2011-11-02 11:00
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- ethics and power Ohlbe 2011-11-01 22:57
- ethics and power Dr_Dan 2011-11-01 13:10
- ethics and power ElMaestro 2011-11-01 13:53
- When does power become unethical? Dr_Dan 2011-11-02 10:55
- When does power become unethical? ElMaestro 2011-11-02 12:01
- When does power become unethical? Dr_Dan 2011-11-02 10:55
- ethics and power ElMaestro 2011-11-01 13:53
- ethics and power d_labes 2011-11-01 11:28
- ethics and power ElMaestro 2011-11-01 10:46
- When is a BE study futile? Dr_Dan 2011-10-31 09:46
Ing. Helmut Schütz