fitNMDS-package: The fitNMDS Package for Evaluating Nonmetric Multidimensional...

Description Details

Description

Measures of agreement for bootstrapped and reciprocal NMDS.

Details

Combining two different datasets into one nonmetric multidimensional scaling (NMDS) model can be risky if they each cover different attribute spaces (e.g., different species pools in ecology). Therefore, comparing two datasets requires estimating internal agreement (sampling variability) relative to external agreement (exchangeability).

Resampled NMDS with resamp_nmds estimates internal agreement (sampling variability) of one candidate dataset. The premise of this is to resample dissimilarities (either through jackknife or bootstrap resampling), perform NMDS ordination on each resampled replicate, then determine collective agreement across all NMDS solutions. Other uses of resampled NMDS may include estimating confidence regions for ordination site scores, or testing the stability of species positions along ordination axes.

Reciprocal NMDS with recip_nmds estimates external agreement (exchangeability) of two candidate datasets. The premise of reciprocal NMDS is to calibrate each of two models with each respective dataset, mutually exchanging datasets among the alternative ordination models, then determining measures of how well each dataset fit the alternative model. This is really just a special case of 2-fold cross-validation as applied to NMDS. The primary use of reciprocal NMDS is to test the null hypothesis that two multivariate datasets are exchangeable.


phytomosaic/fitNMDS documentation built on May 17, 2019, 8:19 p.m.