[R] reference for logistic regression
Robin Hankin
r.hankin at noc.soton.ac.uk
Thu Oct 11 14:43:08 CEST 2007
> [snip]
>
> Whenever you use wikipedia you should be cautious of the quality of
> the information in the articles. Generally the articles are good as a
> brief introduction but they can and do contain errors so you should
> check important facts and not take them at face value. A person in
> one of my classes asked about the standard deviation and I suggested
> that they look at the wikipedia article on the topic. Then I looked
> at it myself and saw that one of the things mentioned is that the
> standard deviation of the Cauchy distribution is undefined, which is
> true, but the reason given is because E[X] is undefined, which is not
> true.
>
The variance page has
<quote>
Many distributions, such as the Cauchy distribution, do not have a
variance because the relevant integral diverges. In particular, if a
distribution does not have an expected value, it does not have a
variance either. The converse is not true: there are distributions
for which the expected value exists, but the variance does not.
</quote>
which seems to be right.
I'd say that A => B but B =/> A together with A being true would be
expressed as "B is true because of A" which is pretty much what the
standard deviation page
says. Is this what you meant?
--
Robin Hankin
Uncertainty Analyst
National Oceanography Centre, Southampton
European Way, Southampton SO14 3ZH, UK
tel 023-8059-7743
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