[R] Bootstrapping confidence intervals

Ista Zahn istazahn at gmail.com
Wed Oct 21 14:40:06 CEST 2009

John Fox has a nice explanation here:


On Wed, Oct 21, 2009 at 6:38 AM, Charlotta Rylander <zcr at nilu.no> wrote:
> Hello,
> We are a group of PhD students working in the field of toxicology. Several
> of us have small data sets with N=10-15. Our research is mainly about the
> association between an exposure and an effect, so preferrably we would like
> to use linear regression models. However, most of the time our data do not
> fulfill the model assumptions for linear models ( no normality of y-varible
> achieved even after log transformation). We have been told that we can use
> bootstrapping to derive a confidence interval for the original parameter
> estimate ( Beta 1)  from the linear regression model and if the confidence
> interval do not include 0, we can "trust" the result from the original
> linear model ( of couse only if a scatter plot of the variables looks ok).
> What is your opinion about this method? Is that ok?  I have problems
> understanding how it is possible to resample several times from an already
> poor distribution ( that do not fulfill the model assumptions for linear
> models) to achieve a confidence interval that "validates" the use of these
> linear models? I would really appriciate a simple explanation about this!
> Many thanks,
> Charlotta Rylander
>        [[alternative HTML version deleted]]
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Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology

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