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Re: st: about residuals and coefficients
From
Ronan Conroy <[email protected]>
To
"<[email protected]>" <[email protected]>
Subject
Re: st: about residuals and coefficients
Date
Sat, 7 Sep 2013 11:22:34 +0000
On 2013 MFómh 7, at 01:42, David Hoaglin wrote:
> Most experiments in social science cannot collect data that allows all
> variables to be held constant. A good design, however, may include
> all combinations of two or more factors, so that one can study the
> effect of one factor without changing the other factors. Usually,
> many additonal variables can only be observed. Those are analyzed as
> covariates (and adjusted for).
I don't tend to believe in this. It implies that the same experimental units are studied under constant conditions, while in real life we study experimental units treated as identical (Wistar rats, for example) under conditions are are not really constant but in which random variation is tolerated (exact site of injection, nearness of rats' cage to radio playing some awful music all day…)
Experiments in the prediction of lifespan of genetically identical roundworms observed in a controlled environment have consistently failed to predict lifespan based on any observable data such as nutrient intake, energy expenditure etc.
See the brilliantly-argued paper by George Davey Smith -
Davey Smith, G. Epidemiology, epigenetics and the “Gloomy Prospect”: embracing randomness in population health research and practice. Int J Epidemiol. 2011 Jun;40(3):537–62.
Ronán Conroy
[email protected]
Associate Professor
Division of Population Health Sciences
Royal College of Surgeons in Ireland
Beaux Lane House
Dublin 2
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