Bioequivalence and Bioavailability Forum • CVintra

CVintra < CVtotal? [Power / Sample Size]

posted by Helmut – Vienna, Austria, 2013-10-07 16:14 (4638 d 03:51 ago) – Posting: # 11618
Views: 8,996

Hi Anu,

❝ Calculated the Intrasubject CV(%) came out 5.83 % (yes its very low).

I’m still not sure whether your calculations are correct. You got a total CV of ~1.4% which is smaller than CV_intra? BTW, a CV_intra of 5.83% for phosphate excretion in urine is hardly to believe.

❝ With the help of Fartssie Sample Size Calculation sheet and R-Software, I find sample size. For this study I have added the values of SD(0.17) & Difference (0.69) in the equivalence crossover and got sample size 5.

Haven’t used FARTSSIE.xls for ages, but you need the CV, not the SD. However,

library(PowerTOST)

sampleN.TOST(logscale=FALSE, theta0=-0.69, theta1=-2.45, theta2=2.45, CV=0.0583)

+++++++++++ Equivalence test - TOST +++++++++++

            Sample size estimation

-----------------------------------------------

Study design:  2x2 crossover 

untransformed data (additive model)



alpha = 0.05, target power = 0.8

BE margins        = -2.45 ... 2.45

Null (true) diff. = -0.69,  CV = 0.0583



Sample size (total)

 n     power

4   1.000000

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Complete thread:

Sample Size Anu 2013-09-04 07:03
- Sample Size Dr_Dan 2013-09-04 09:52
- Linear model and Fieller… Helmut 2013-09-04 13:20
  - Linear model and Fieller… jag009 2013-09-04 17:23
    - Linear model and Fieller… Anu 2013-10-04 13:16
      - Linear model and 80–120% Helmut 2013-10-04 15:20
        
        Linear model and 80–120% Anu 2013-10-07 09:59
        
        CVintra < CVtotal?Helmut 2013-10-07 14:14