Message-ID: <alpine.LMD.2.00.1509161120170.20194@orpheus.qimr.edu.au>
Date: 2015-09-16T01:29:03Z
From: David Duffy
Subject: Logit mixed model power analysis
In-Reply-To: <5A718A87-705B-4879-AD6F-16D5163C43EB@glasgow.ac.uk>
On Wed, 16 Sep 2015, Paul Johnson wrote:
> I second what Thierry said about the pointlessness of post-hoc power
> analysis when using the observed effect size.
>>
>> Post-hoc power tests are not very informative. You will get a high
>> power when the signal is significant and low power when not
>> significant.
A few people defend it as an estimate of the reproducibility
probability. Gelman and Carlin suggest plugging in a "sensible"
(Bayesian) estimate of the true effect based on your prior knowledge, so
you can estimate the probability of a "Type S" (sign of true effect
could actually be opposite to your study point estimate) or "Type M"
error.
Cheers, David.
| David Duffy (MBBS PhD)
| email: David.Duffy at qimrberghofer.edu.au ph: INT+61+7+3362-0217 fax: -0101
| Genetic Epidemiology, QIMR Berghofer Institute of Medical Research
| 300 Herston Rd, Brisbane, Queensland 4006, Australia GPG 4D0B994A