On Thu, 2011-11-17 at 10:01 +0100, gabriel singer wrote: > ... dangerous wording, there could in fact be a location effect of > 'location' and/or a dispersion effect of 'location'.
Well of course, but I was assuming that the assumptions of the test were met! ;-) > Gian, I suggest you add a test of a dispersion effect using the function > betadisper(), then you know a bit more about the type of effect. Indeed, and as the author of that function I too would suggest that the homogeneity assumption be tested. G > gabriel > > On 11/16/11 11:02 PM, Gavin Simpson wrote: > > On Wed, 2011-11-16 at 03:43 +0100, Gian Maria Niccolò Benucci wrote: > >> Hi all, > >> > >> I had 84 samples collected in 7 different sites. > >> In each sample were individuated the different fungal species and recorded. > >> I would test if exist a real difference between the sites and if exist a > >> sort of site effect that structure the fungal communities... > >> Then, I did adonis test > >> > >>> adonis(community.sq ~ location, data=env.table, permutations=999) > >> Call: > >> adonis(formula = community.sq ~ location, data = env.table, permutations = > >> 999) > >> > >> Df SumsOfSqs MeanSqs F.Model R2 Pr(>F) > >> location 6 12.593 2.09886 6.8867 0.34922 0.001 *** > >> Residuals 77 23.467 0.30477 0.65078 > >> Total 83 36.060 1.00000 > >> --- > >> Signif. codes: 0 *** 0.001 ** 0.01 * 0.05 . 0.1 1 > >> > >> > >> > >> The significance is R2=0.349 at P=0.001 > >> Can I assure that exist a strong site effect in structuring the communities > >> in each site? > > Depends. The test is one of no effect of `location`. You have found > > evidence against this hypothesis and thus could reject this hypothesis, > > instead accepting the alternative hypothesis that there is an effect of > > `location`. As to the strength of this effect? ~35% of the sums of > > squares can be explained by `location`. Substantially more of the > > variance remains unexplained. As I know nothing about your subject area, > > I am unable to comment further on the strength of the relationship. > > > > Seeing as many ecologists whose work I read would say an effect is > > significant if the p-value was>= 0.05. Not that I subscribe to this way > > or working, but by that criterion, you have identified a significant > > `location` effect. > > > > HTH > > > > G > > > >> Thanks for helping, > >> > >> G. > >> > >> [[alternative HTML version deleted]] > >> > >> _______________________________________________ > >> R-sig-ecology mailing list > >> [email protected] > >> https://stat.ethz.ch/mailman/listinfo/r-sig-ecology > -- %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% Dr. Gavin Simpson [t] +44 (0)20 7679 0522 ECRC, UCL Geography, [f] +44 (0)20 7679 0565 Pearson Building, [e] gavin.simpsonATNOSPAMucl.ac.uk Gower Street, London [w] http://www.ucl.ac.uk/~ucfagls/ UK. WC1E 6BT. [w] http://www.freshwaters.org.uk %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% _______________________________________________ R-sig-ecology mailing list [email protected] https://stat.ethz.ch/mailman/listinfo/r-sig-ecology
