> [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 ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
