Power of two stage design [Power / Sample Size]
Dear Pjs,
This is a fundamental misunderstanding.
What you try to do is, if I understand you correctly, to obtain the power of a two stage design.
This is not possible in FARTSSIE and also not in the R package
The framework of TSDs is so complicated that no algebraic solution for obtaining power is available. What you have to do is to use simulations, like the ones described in the Potvin paper.
Have a look into the R add-on package
Example:
gives
gives
BTW: If you aim to work exactly like Potvin et al. you have to set the argument
Nevertheless you will not obtain exacly the same numbers due to the unknown auxillary conditions for the simulations like e.g. the seed of the random number genarator or its type.
BTW2: The negative power from FARTSSIE is of course nonsense and results from an approximation for the power calculation. The exact power for a fixed (1-stage) design with your settings is
❝ Currently i am cross verifying power value with the published paper of the potvin for two stage. They had calculated power with modification of Hauschke et al. For example if i take N=12, CV=40% and ratio 95% power by method C is reported to be 0.7505. For the same parameters power by FARTSSIE is -24.19%.
This is a fundamental misunderstanding.
What you try to do is, if I understand you correctly, to obtain the power of a two stage design.
This is not possible in FARTSSIE and also not in the R package
PowerTOST
.The framework of TSDs is so complicated that no algebraic solution for obtaining power is available. What you have to do is to use simulations, like the ones described in the Potvin paper.
Have a look into the R add-on package
Power2Stage
. With the function power.2stage()
you are able to verify the type 1 error and the power reported in the Potvin paper.Example:
library(Power2Stage)
# power at true ratio=0.95
power.2stage(alpha=c(0.0294, 0.0294), method="C", CV=0.4, n1=12, GMR=0.95, theta0=0.95)
gives
TSD with 2x2 crossover
Method C: alpha0 = 0.05, alpha (s1/s2) = 0.0294 0.0294
Target power in power monitoring and sample size est. = 0.8
Power calculation via non-central t approx.
CV1 and GMR = 0.95 in sample size est. used
No futility criterion
BE acceptance range = 0.8 ... 1.25
CV = 0.4; n(stage 1) = 12; GMR= 0.95
1e+05 sims at theta0 = 0.95 (p(BE) = 'power').
p(BE) = 0.75058
p(BE) s1 = 0.00986
Studies in stage 2 = 98.95%
Distribution of n(total)
- mean (range) = 78.9 (12 ... 302)
- percentiles
5% 50% 95%
32 74 142
# empirical type 1 error
power.2stage(alpha=c(0.0294, 0.0294), method="C", CV=0.4, n1=12, GMR=0.95, theta0=1.25)
gives
TSD with 2x2 crossover
Method C: alpha0 = 0.05, alpha (s1/s2) = 0.0294 0.0294
Target power in power monitoring and sample size est. = 0.8
Power calculation via non-central t approx.
CV1 and GMR = 0.95 in sample size est. used
No futility criterion
BE acceptance range = 0.8 ... 1.25
CV = 0.4; n(stage 1) = 12; GMR= 0.95
1e+06 sims at theta0 = 1.25 (p(BE) = TIE 'alpha').
p(BE) = 0.034468
p(BE) s1 = 0.003881
Studies in stage 2 = 99.5%
Distribution of n(total)
- mean (range) = 79.1 (12 ... 360)
- percentiles
5% 50% 95%
32 74 142
BTW: If you aim to work exactly like Potvin et al. you have to set the argument
pmethod="shifted"
in the function calls. This calculates power in the power monitoring step of the two stage schemes via a somewhat crude approximation and was used in the Potvin paper for speed reasons only.Nevertheless you will not obtain exacly the same numbers due to the unknown auxillary conditions for the simulations like e.g. the seed of the random number genarator or its type.
BTW2: The negative power from FARTSSIE is of course nonsense and results from an approximation for the power calculation. The exact power for a fixed (1-stage) design with your settings is
library(PowerTOST)
power.TOST(CV=0.4, n=12)
[1] 0.02843316
—
Regards,
Detlew
Regards,
Detlew
Complete thread:
- Power R WinNonLin Yura 2018-01-23 15:02
- Power R WinNonLin d_labes 2018-01-23 15:25
- Power_TOST in PHX/WNL 6.4+ Helmut 2018-01-23 16:05
- Power_TOST in PHX/WNL 6.4+ d_labes 2018-01-23 16:54
- Power_TOST in PHX/WNL 6.4+ Helmut 2018-01-23 17:25
- Power_TOST in PHX/WNL 6.4+ Yura 2018-01-23 21:55
- Power_TOST in PHX/WNL 6.4+ d_labes 2018-01-23 16:54
- Power_TOST in PHX/WNL 6.4+ Helmut 2018-01-23 16:05
- Power R WinNonLin pjs 2018-03-23 10:41
- Power of two stage designd_labes 2018-03-23 17:02
- Power2Stage / power.2stage() Helmut 2018-03-24 15:49
- Power R WinNonLin d_labes 2018-01-23 15:25