decostand {vegan} | R Documentation

## Standardizaton Methods for Community Ecology

### Description

The function provides some popular (and effective) standardization methods for community ecologists.

### Usage

    decostand(x, method, MARGIN, range.global, na.rm = FALSE)
    wisconsin(x)

### Arguments

`x` | Community data matrix.
`method` | Standardization method.
`MARGIN` | Margin, if default is not acceptable.
`range.global` | Matrix from which the range is found in `method = "range"`. This allows using same ranges across subsets of data. The dimensions of `MARGIN` must match with `x`.
`na.rm` | Ignore missing values in row or column standardizations.

### Details

The function offers following standardization methods for community data:

- `total`: divide by margin total (default `MARGIN = 1`).
- `max`: divide by margin maximum (default `MARGIN = 2`).
- `freq`: divide by margin maximum and multiply by number of non-zero items, so that the average of non-zero entries is one (Oksanen 1983; default `MARGIN = 2`).
- `normalize`: make margin sum of squares equal to one (default `MARGIN = 1`).
- `range`: standardize values into range 0 ... 1 (default `MARGIN = 2`). If all values are constant, they will be transformed to 0.
- `standardize`: scale into zero mean and unit variance (default `MARGIN = 2`).
- `pa`: scale into presence/absence scale (0/1).
- `chi.square`: divide by row sums and square root of column sums, and adjust for square root of matrix total (Legendre & Gallagher 2001). When used with Euclidean distance, the matrix should be similar to the the Chi-square distance used in correspondence analysis. However, the results from `cmdscale` would still differ, since CA is a weighted ordination method (default `MARGIN = 1`).
- `hellinger`: square root of `method = "total"` (Legendre & Gallagher 2001).

Standardization, as contrasted to transformation, means that the entries are transformed relative to other entries.

All methods have a default margin. `MARGIN=1` means rows (sites in a normal data set) and `MARGIN=2` means columns (species in a normal data set).

Command `wisconsin` is a shortcut to common Wisconsin double standardization where species (`MARGIN=2`) are first standardized by maxima (`max`) and then sites (`MARGIN=1`) by site totals (`tot`).

Most standardization methods will give non-sense results with negative data entries that normally should not occur in the community data. If there are empty sites or species (or constant with `method = "range"`), many standardization will change these into `NaN`.

### Value

Returns the standardized data frame, and adds an attribute `"decostand"` giving the name of applied standardization `"method"`.

### Note

Common transformations can be made with standard R functions.

### Author(s)

Jari Oksanen

### References

Legendre, P. & Gallagher, E.D. (2001) Ecologically meaningful transformations for ordination of species data. Oecologia 129: 271–280.

Oksanen, J. (1983) Ordination of boreal heath-like vegetation with principal component analysis, correspondence analysis and multidimensional scaling. Vegetatio 52, 181–189.

### Examples

    data(varespec)
    sptrans <- decostand(varespec, "max")
    apply(sptrans, 2, max)
    sptrans <- wisconsin(varespec)
    # Chi-square: Similar but not identical to Correspondence Analysis.
    sptrans <- decostand(varespec, "chi.square")
    plot(procrustes(rda(sptrans), cca(varespec)))

[Package vegan version 1.8-6 Index]