Dear Siegfried, you could find fBasics at this web address:
http://cran.at.r-project.org/src/contrib/Descriptions/fBasics.html it includes skewness() and kurtosis() function. I usually run R on WIN 2000 and I don't know MAC! I can suggest to use Kolgomorov-Smirnov test to test whether the data would fit to a gamma-distribution ? ks.test and this web page for theory about ks test: http://www.itl.nist.gov/div898/handbook/eda/section3/eda35g.htm Having mean and median quite similar don't mean it's a normal distribution, but, maybe, could be only a simmetric distribution! Best Vito --- Siegfried Gonzi <[EMAIL PROTECTED]> ha scritto: > Hi: > > Thanks for your answer. > > Do you know how to test whether the data would fit > to a gamma-distribution? > > How can I call fBasics? > > Note: I installed R-language on my Macintosh today; > I have used the > binary -- pre compiled -- package. > > Some of the R-help facilties do not function on my > Mac. > > Again to my data: How can I compute the skew? I > think I lack some basic > packages - right? > > The curious things actually is that the median and > the mean are quite > similar, e.g. 0.19 and 0.2 respectively; the skew is > about 1.0 (I > calculated the skew by my own computer code in > Bigloo). > > The problem actually is: my boss expects from me > that I make some tests; > personally I am a bit generous and everything is a > Gaussian or > log-Gaussian distribution, because how can I be sure > that the underlying > data to not have any serious flaws? Statistics is > black art - right? > > Regards, > S. Gonzi > > > > Vito Ricci wrote: > > >Hi, > > > >from what you're writing: > >"The logaritmic transformation > >"shapiro.test(log10(y))" says: W=0.9773, p-value= > >2.512e-05." it seems the log-values are not > >distributed normally and so original data are not > >distributed like a log-normal: the p-value is > >extremally small! > > > >Other tests for normality are available in package: > >nortest > > > >compare the log-transformation of your ecdf with > >normal cdf: see ? ecdf > > > >use qqnorm and qqplot > > > >did you calculate skewness and kurtosis? see in > >package fBasics. > > > >I remember to you that the log-normal distribution > as > >three parameters: shape parameter, location > parameter > >and scale parameter. Transfroming by the simple > log, > >you are missing the location parameter, or > implicitely > > you assuming is =0. > > > >See: > >http://www.itl.nist.gov/div898/handbook/eda/section3/eda3669.htm > >for more news about log-normal distribution. > > > >I hope I give you a little help. > >Best > >Vito > > > > > > > > > >you wrote: > > > >Hello: > > > >Yes I know that sort of questions comes up quite > >often. But with all due > >respect I din't find how to perform what I want. I > am > >searching archives > >and bowsing manuals but it isn't there, though, it > is > >a ridiculous > >simple task for the experienced R user. > > > >I have data and can do the following with them: > > > >== > >hist(y, prob=TRUE) > >lines(density(y,bw=0.03) > >== > > > >The result actually is a nice histogram > superimposed > >by a line plot. > > > >The histogram is a bit skewed to the left. My > >assumption actually is > >that a log-normal transformation would cure the > >problem. But how the > >hell can one plot such a density function or > Gaussian > >function which has > >logarithmic scales on x axis. > > > >For example I tried: > > > >== > >plot(hist(y),log="x") > > > >or > > > >plot(hist(log10(y)),log="x") > >== > > > >But with no avail. I want my axis like: 1,10,100 > > > > > > > >What would be other methods to test whether the > data > >are logaritmically > >distributed. > > > >A last question to the Shapiro-Wilk test. Were can > I > >get critical > >parameters? I mean I get for my distribution: > >W=0.9686, p-value=6.887e-07. > >What does that mean? Yes I have got some books > about > >statics, but none > >of them says what one should do with the values > then. > >The logaritmic > >transformation "shapiro.test(log10(y))" says: > >W=0.9773, p-value= 2.512e-05. > > > >Sorry for disturbing you. Although, it is really no > >homework. I need it > >for my Phd in physics; after a lengthy computation > on > >the computer I > >would like to go to see whether the outputs are > >log-normal or normal > >distributed. > > > >Regards, > >Siegfried Gonzi > >== > >University of Graz > >Institute for Physics > >Tel.: ++43-316-380-8620 > > > >===== > >Diventare costruttori di soluzioni > >Became solutions' constructors > > > >"The business of the statistician is to catalyze > >the scientific learning process." > >George E. P. Box > > > > > >Visitate il portale http://www.modugno.it/ > >e in particolare la sezione su Palese > http://www.modugno.it/archivio/cat_palese.shtml > > > > > > > >___________________________________ > Audibles, Avatar, Webcam, Giochi, Rubrica... > Scaricalo ora! > >http://it.messenger.yahoo.it > > > > > > > > ===== Diventare costruttori di soluzioni Became solutions' constructors "The business of the statistician is to catalyze the scientific learning process." George E. P. Box Visitate il portale http://www.modugno.it/ e in particolare la sezione su Palese http://www.modugno.it/archivio/cat_palese.shtml ______________________________________________ [EMAIL PROTECTED] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html