Michael, so you're suggesting that I should do: aux <- interaction( Topology, Drift, lambda) and then fligner.test(dT~aux)
Is that correct? On Thu, Sep 18, 2008 at 8:32 AM, Michael Dewey <info <at> aghmed.fsnet.co.uk> wrote: > At 16:03 17/09/2008, Javier Acuña wrote: >> >> Hi, I'm a new user of R. My background is Electrical Engineering, so >> please bear with me if this is a silly question. > > For future reference you might find > ?interaction > helpful as another tool in your box. > > >> I'm trying to assess whether the results of an experiment satisfy the >> hypothesis of homoscedasticity (my ultimate goal is to use ANOVA). > > It is hard to resist quoting Box (1953, Biometrika, 40, p333) that these > tests are '... like putting to sea in a rowing boat to find out whether > conditions are safe for an ocean liner to leave port' > >> The result of the experiment is mean delay (dT), which depends on >> three factors, topology, drift, and lambda. The first two factors are >> categorical (with 4 levels each) and the last one is numerical, with >> two levels. >> >> A sample of my data is as follows: >> >> dT Topology Drift lambda >> 258.789 Tree b1 .43 >> 244.195 Tree b1 .43 >> 115.961 Tree b2 .3 >> 115.183 Tree b2 .3 >> >> I would like to separate dT in the 32 samples (4x4x2), and test if the >> variance of each sample is equal to the other 31 samples. >> I tried using fligner.test and bartlett.test, but either test seems to >> only work for one factor: >> >> > fligner.test( dT ~ Topology + Drift + lambda) >> >> Fligner-Killeen test of homogeneity of variances >> >> data: dT by Topology by Drift by lambda >> Fligner-Killeen:med chi-squared = 15.4343, df = 2, p-value = 0.0004451 >> >> > fligner.test( dT ~ Topology ) >> >> Fligner-Killeen test of homogeneity of variances >> >> data: dT by Topology >> Fligner-Killeen:med chi-squared = 15.4343, df = 2, p-value = 0.0004451 >> >> As I see from the previous two outputs, fligner.test only takes into >> account the first factor. Similar results are obtained for >> bartlett.test. >> >> At this point I don't know if I'm using the test incorrectly or >> something else. I would really appreciate any help. I'm using R >> version 2.7.2 (2008-08-25) in Windows XP. >> >> Many thanks in advance >> Javier >> >> ---------------------------------------------------- >> Javier Acuna >> Electrical Engineering Grad Student >> Universidad de Chile >> [EMAIL PROTECTED] > > Michael Dewey > http://www.aghmed.fsnet.co.uk > > ______________________________________________ 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.
