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PERMANOVA and the Behrens-Fisher F statistic #344
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Thanks for the query. Fascinating / interesting paper. Maybe drop Anderson
an email, if you have no luck here.
Much appreciate having it highlighted in the mail.
Best wishes,
Mark
…On Mon, 10 Feb 2020, 18:34 Melanie, ***@***.***> wrote:
I am working with a data set with an unbalanced sampling design that
violates the assumption of homogeneity of group dispersions. I was informed
that one can modify the source code for the adonis() function to calculate
a modified Behrens-Fisher F-statistic per Anderson et al. 2017 (doi:
10.1111/anzs.12176). Has anyone tried this? Is there a version of the
source code already available that can accomplish this task? I was able to
brute force calculate the BFS for a simple, one-variable PERMANOVA based on
the mathematical descriptions provided in the article; however, my
abilities with matrix algebra aren't super sophisticated, so it's been hard
for me to wrap my head around how to calculate the BFS for a PERMANOVA with
multiple variables and interaction effects. Any information the devs or the
community might have about how to code this in R and/or modify the adonis()
function would be super helpful. Thank you!
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You can examine the code for adonis here - https://github.com/jarioksa/vegan/blob/master/R/adonis.R I agree that the solution provided in Anderson et al. 2017 should be implemented in the adonis function. It is currently provided in the PERMANOVA+ module for PRIMER-e. Currently there is no R implementation of this solution that I am aware of. 🙏 any statistical gurus out there want to help out? 🧞♂️ |
If still relevant - I recently emailed PRIMER about this and got a reply from Anderson who said the adjusted F value in the 2017 paper is currently only available in the PRIMER software (as far as she is aware!). If anyone can implement this into the adonis function you're amazing! |
@ecologyjh, it has also been implemented in the Fathom Toolbox in MATLAB (functions f_permanova and f_permanovaPW). |
For a one-way ANOVA with just a standard categorical factor I believe this would calculate the modified F (I'm getting the same modified F as the Fathom Toolbox implementation). I took the beginning of the
Example of Calculating modified F on the dune dataset
|
Hi, will I able to use this code for a 4-way PERMANOVA or just for one-way? |
@pkmnsandy, this is unfortunately just for a one-way PERMANOVA. The Fathom implementation states that this is a "one-way (modified) PERMANOVA" and the original paper states "The F2 test statistic can be extended to allow for differences in dispersions of replicates within sites, and differences in dispersions of site centroids within regions, for relevant tests of individual factors at each spatial scale. Similar extensions can be formulated and derived for tests of individual terms in fixed, random or mixed multi-way ANOVA models including interactions. We shall leave these extensions (beyond the scope of the current contribution) for a future endeavour." |
I am working with a data set with an unbalanced sampling design that violates the assumption of homogeneity of group dispersions. I was informed that one can modify the source code for the adonis() function to calculate a modified Behrens-Fisher F-statistic per Anderson et al. 2017 (doi: 10.1111/anzs.12176). Has anyone tried this? Is there a version of the source code already available that can accomplish this task? I was able to brute force calculate the BFS for a simple, one-variable PERMANOVA based on the mathematical descriptions provided in the article; however, my abilities with matrix algebra aren't super sophisticated, so it's been hard for me to wrap my head around how to calculate the BFS for a PERMANOVA with multiple variables and interaction effects. Any information the devs or the community might have about how to code this in R and/or modify the adonis() function would be super helpful. Thank you!
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