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The Virtual Marchant Subsampler

A macro for Microsoft Excel

Version 2 for Excel 97, and a new version for R

By Chris Walsh
Cooperative Research Centre for Freshwater Ecology
Water Studies Centre
Monash University
Clayton 3800
Australia

These files simulate the box subsampler described by Marchant (1989). Instructions are embedded in the excel files, and are included as help files in the R function. One of the routine's applications is demonstrated in Walsh (1997). Please cite this latter paper if you use the macro or the function.

For some additional thoughts on subsampling subsequent to Walsh (1997), click here

A new version of this utility, with added features, is now available for the statistical language and environment 'R'.

This link contains R code for four subsampling functions:

sub.sample, a simulated 100-cell box subsampler

ssN, a fixed number subsampler

ssN.nr, a repeated fixed number subsampler without replacement

rarefact, a rarefaction estimator of species richness

To use the code, save it as "sub.sample.R" in R's working directory, and enter

source(“sub.sample.R”)

If you also save the file urban.txt in the working directory, the examples in the above help pages will work.

The new sub.sample function allows more flexibility, by allowing subsampling of multiple samples at once (arranged as a sample x taxon matrix).
It is also more atutomated than the Excel macros, allowing an a-priori selection of a fixed number, fixed proportion or a conditional subsampling strategy. Unlike the Excel macros, it does not allow repeated subsampling without replacement. The function ssN.nr allows this.

See CRAN for more information about R.

To download the macro (for Excel 97, size 170K), virtsmssv2.xls.

References

  • Marchant, R. (1989). A subsampler for samples of benthic macroinvertebrates. Bulletin of the Australian Society for Limnology 12, 49-52.
  • Walsh, C. J. (1997). A multivariate method for determining optimal subsample size in the analysis of macroinvertebrate samples. Marine and Freshwater Research 48(3), 241-8. (abstract)
  

 

Urban Water Ecology