## Optimists and pessimists [Power / Sample Size]

Hi David,

» I think the answer to the first question of this post is "because you were very pessimistic on your assumptions regarding sample size" which is something very common in BABE trials (at least, this is my perception).

Ha-ha! I got too many failed studies on my desk and my clients think that I’m Jesus and can reanimate a corpse… In most cases they were overly

» In this case, given your simulations above and the expected probability of approximately 12% of the studies having power greater then 95% …

~15%!

» … having in consideration the initial assumptions, post hoc power means nothing.

Yep.

» But if you had 100 studies instead and 90% of the had >95% power although the sample size was calculated assuming expected power of 80%, some questions and conclusions might be drawn from those results, don't you think?

Agree.

» From my understanding of the initial question, this was the case found. So I think that they should start by reviewing how they define their assumptions for the sample size, namely why they assume GMR=1.10 instead of the "normal" 0.95/1.05.

Well, the current GL is poorly written. Talks only about an “appropriate sample size calculation” [sic]. The 2001 NfG was more clear:

I’m not a pessimist,

I’m just a well informed optimist.

To call the statistician after the experiment is done

may be no more than asking him to perform a postmortem examination:

he may be able to say what the experiment died of.

OK, I make money acting as a coroner. Wasn’t really successful in the reanimation-attempts.

» I think the answer to the first question of this post is "because you were very pessimistic on your assumptions regarding sample size" which is something very common in BABE trials (at least, this is my perception).

Ha-ha! I got too many failed studies on my desk and my clients think that I’m Jesus and can reanimate a corpse… In most cases they were overly

*optimistic*in designing their studies.» In this case, given your simulations above and the expected probability of approximately 12% of the studies having power greater then 95% …

~15%!

» … having in consideration the initial assumptions, post hoc power means nothing.

Yep.

» But if you had 100 studies instead and 90% of the had >95% power although the sample size was calculated assuming expected power of 80%, some questions and conclusions might be drawn from those results, don't you think?

Agree.

» From my understanding of the initial question, this was the case found. So I think that they should start by reviewing how they define their assumptions for the sample size, namely why they assume GMR=1.10 instead of the "normal" 0.95/1.05.

Well, the current GL is poorly written. Talks only about an “appropriate sample size calculation” [sic]. The 2001 NfG was more clear:

The number of subjects required is determined by

- the error variance associated with the primary characteristic to be studied as estimated from a pilot experiment, from previous studies or from published data,

- the significance level desired,

- the expected deviation from the reference product compatible with bioequivalence (∆) and

- the required power.

*both*T and R. Given that power is most sensitive to the GMR, I question the usefulness of 0.95.I’m not a pessimist,

I’m just a well informed optimist.

*José Saramago*To call the statistician after the experiment is done

may be no more than asking him to perform a postmortem examination:

he may be able to say what the experiment died of.

*R.A. Fisher*OK, I make money acting as a coroner. Wasn’t really successful in the reanimation-attempts.

—

Cheers,

Helmut Schütz

The quality of responses received is directly proportional to the quality of the question asked. ☼

Science Quotes

Cheers,

Helmut Schütz

The quality of responses received is directly proportional to the quality of the question asked. ☼

Science Quotes

### Complete thread:

- Power is getting high - kms.srinivas, 2017-12-26 07:39
- Power is getting high? - d_labes, 2017-12-26 12:08
- Stop estimating post hoc power! - Helmut, 2017-12-26 12:22
- Stop estimating post hoc power! - kms.srinivas, 2017-12-26 13:00
- Stop estimating post hoc power! - ElMaestro, 2017-12-26 14:11
- Simulations - Helmut, 2017-12-26 15:51
- Simulations - BE-proff, 2017-12-27 06:53
- Simulations - ElMaestro, 2017-12-27 07:25
- Simulations - Yura, 2017-12-27 08:23
- Simulations - kms.srinivas, 2017-12-27 09:11
- Simulations - Yura, 2017-12-27 10:07
- α and 1–β - Helmut, 2017-12-27 12:57
- α and 1–β - Yura, 2017-12-27 13:33
- α and 1–β - Helmut, 2017-12-27 14:31
- α and 1–β - Yura, 2017-12-28 06:50
- Educate the IEC and regulators - Helmut, 2017-12-28 11:30

- α and 1–β - Yura, 2017-12-28 06:50

- α and 1–β - Helmut, 2017-12-27 14:31

- α and 1–β - Yura, 2017-12-27 13:33

- α and 1–β - Helmut, 2017-12-27 12:57
- “Forced BE” 101 - Helmut, 2017-12-27 12:23
- “Forced BE” 101 - kms.srinivas, 2017-12-27 12:41
- Would you be so kind answering our questions? - Helmut, 2017-12-27 13:02
- Would you be so kind answering our questions? - kms.srinivas, 2017-12-28 05:53
- Yes, but why? - Helmut, 2017-12-28 11:47
- Yes, but why? - DavidManteigas, 2017-12-28 16:59
- Optimists and pessimists - Helmut, 2017-12-28 17:33
- "normal" GMR setting - d_labes, 2017-12-28 18:57
- Example for discussion - mittyri, 2017-12-28 22:06
- Example for discussion - Helmut, 2017-12-28 22:33

- I prefer to play it safe - Helmut, 2017-12-28 22:10

- Example for discussion - mittyri, 2017-12-28 22:06

- "normal" GMR setting - d_labes, 2017-12-28 18:57
- Full ACK - d_labes, 2017-12-28 17:41
- About GMR 1.10 - kms.srinivas, 2017-12-29 13:20
- Better 0.95 or 0.90 - Helmut, 2017-12-29 16:18

- Optimists and pessimists - Helmut, 2017-12-28 17:33
- Yes, but why? - Yura, 2017-12-29 13:46
- Buffon's needle - Astea, 2018-01-20 23:55
- Buffon's needle - Oleg777, 2018-10-09 22:48
- 0.95 or 1.05 - Helmut, 2018-10-10 13:41

- Buffon's needle - Helmut, 2018-10-10 12:46
- Buffon's needle - Astea, 2018-10-11 23:14
- School maths - Helmut, 2018-10-12 01:10
- School russian - Astea, 2018-10-12 12:41
- Offtop: Umschrift der westlichen Eigennamen auf Russisch - mittyri, 2018-10-12 23:25

- School maths - Helmut, 2018-10-12 01:10

- Buffon's needle - Astea, 2018-10-11 23:14

- Buffon's needle - Oleg777, 2018-10-09 22:48

- Yes, but why? - DavidManteigas, 2017-12-28 16:59

- Yes, but why? - Helmut, 2017-12-28 11:47
- EEU? - mittyri, 2017-12-28 21:52
- EEU? - Yura, 2017-12-29 13:41
- EEU - pharmacokinetic equation??? - mittyri, 2017-12-29 14:11

- EEU? - Beholder, 2018-01-16 15:10

- EEU? - Yura, 2017-12-29 13:41

- Would you be so kind answering our questions? - kms.srinivas, 2017-12-28 05:53

- Would you be so kind answering our questions? - Helmut, 2017-12-27 13:02

- “Forced BE” 101 - kms.srinivas, 2017-12-27 12:41

- Simulations - Yura, 2017-12-27 10:07

- Simulations - kms.srinivas, 2017-12-27 09:11
- Simulations - xtianbadillo, 2018-01-18 22:22

- Simulations - BE-proff, 2017-12-27 06:53

- Stop estimating post hoc power! - kms.srinivas, 2017-12-26 13:00
- Numbers don't lie - ElMaestro, 2017-12-28 20:13