Bioequivalence and Bioavailability Forum • Basic maths

Basic maths [Power / Sample Size]

posted by Helmut – Vienna, Austria, 2014-11-07 21:09 (3825 d 02:48 ago) – Posting: # 13844
Views: 17,391

Hi Monica,

❝ Sorry if I posted my question on the wrong place (first time posting on this forum).

No problem; welcome to the club!

❝ I used the formula presented on slides 25-26 on a clinical protocol as justification for sample size calculation and the mexican regulatory agency asked for a scientific justification …

Oh no! I derived it on my own ages ago. That’s 8^th grade maths. Any 14 year old kid should be able to do it. I’m not aware of any reference.

❝ … or a bibliography where the robustness of the formula can be proved/demosntrated.

The formula is exact if the study is balanced (n_TR = n_RT = ½N). Sometimes you don’t know whether a study was balanced (only the total number of completers given). If N is odd, it was imbalanced for sure. If N is even, you have no clue. Have a look at my example (slide 29). The study was extremely imbalanced (16:8) and the true CV 24.74%. But you don’t know that (only N 24 given). For any given combination of subjects in sequences you would estimate a CV which is higher than the true one. In other words, if you plan a study based on the estimate the sample size will be higher than required. You loose money, but don’t risk to be underpowered.

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Helmut Schütz

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Complete thread:

minimum number of subject in bioequivalence study khaoula 2014-09-27 11:14
- minimum number of subject in bioequivalence study ElMaestro 2014-09-27 11:26
  - minimum number of subject in bioequivalence study khaoula 2014-09-27 23:49
    - “Overpowered” studies due to GLs Helmut 2014-09-28 01:13
      - “Overpowered” studies due to GLs khaoula 2014-09-28 22:36
        
        “Overpowered” studies due to GLs Helmut 2014-09-29 03:51
      - Scientific Validation for the Sample Size Formula mreyes 2014-11-07 19:47
        
        Basic mathsHelmut 2014-11-07 20:09
        
        Basic maths mreyes 2014-11-07 20:47
        
        Reference for CI ⇒ MSE Helmut 2014-12-14 01:51
        
        Reference for CI ⇒ MSE mreyes 2015-02-19 19:50
        
        Failed study: power <80%! Helmut 2015-02-20 19:09
        
        Failed study: power <80%! mreyes 2015-02-23 17:07
        
        Reported 99.98%, correct 1.4% Helmut 2015-02-23 17:38
        
        Reported 99.98%, correct 1.4% ElMaestro 2015-02-23 17:51
        
        GMR ∉ AR ⇒ power <5% Helmut 2015-02-24 01:33
        
        GMR ∉ AR ⇒ power <5% mreyes 2015-02-24 17:34