bas {OLIN} | R Documentation

## Between-array scaling

### Description

This function performs an between-array scaling

### Usage

    bas(obj,mode="var")

### Arguments

`obj` | object of “marrayNorm”
`mode` | mode of scaling. Default option is scaling of arrays to have the same within-array variance of logged ratios (`var`). Alternatively, `mad` `qq` can be used (see details)

### Details

The function `bsv` adjust the scale of logged ratios (`M=(log2(Ch2)-log2(Ch1))`) between the different arrays stored in `obj`.

Following schemes (`mode`) are implemented:

- `mode="var"`: Logged ratios `M` are scaled to show the same (within-array) variance for all arrays in the batch stored in `obj`. The variance is calculated using `var`.
- `mode="mad"`: The same procedure as for `mode="var"` is applied using, however, median absolute deviation (`mad`) as robust estimate for withing-array variance.
- `mode="qq"`: The quantile scaling is using the same procedure as the quantile normalisation described by Bolstad et al. (2003). In brief: Given X is the matrix with logged ratios (column corresponding to arrays, rows to genes)
  1. Sort each column of X (independently) producing Xs,
  2. Replace values in each row of Xs by the mean value of the row producing Xsm,
  3. Rearrange the ordering for each column of matrix Xsm, so that it has the columns have same ordering as for the original matrix X.
  The last step yields the scaled logged ratios `M`.

### Note

Between-array scaling should only be performed if it can be assumed that the different arrays have a similar distribution of logged ratios. This has to be check on a case-by-case basis. Caution should be taken in the interpretation of results for arrays hybridised with biologically divergent samples, if between-array scaling is applied.

### Author(s)

Matthias E. Futschik (http://itb.biologie.hu-berlin.de/~futschik)

### References

Bolstad et al., A comparison of normalization methods for high density oligonucleotide array data based on variance and bias, Bioinformatics, 19: 185-193, 2003

### See Also

`marrayNorm`,`var`,`mad`

### Examples

    # DISTRIBUTION OF M BEFORE SCALING
    data(sw.olin)

    col <- c("red","blue","green","orange")
    M <- maM(sw.olin)

    plot(density(M[,4]),col=col[4],xlim=c(-2,2))
    for (i in 1:3){
      lines(density(M[,i]),col=col[i])
    }

    # SCALING AND VISUALISATION
    sw.olin.s <- bas(sw.olin,mode="var")

    M <- maM(sw.olin.s)

    plot(density(M[,4]),col=col[4],xlim=c(-2,2))
    for (i in 1:3){
      lines(density(M[,i]),col=col[i])
    }

[Package OLIN version 1.18.0 Index]