contrMat function

Contrast Matrices

Computes contrast matrices for several multiple comparison procedures.

contrMat(n, type = c("Dunnett", "Tukey", "Sequen", "AVE", 
                     "Changepoint", "Williams", "Marcus", 
                     "McDermott", "UmbrellaWilliams", "GrandMean"), 
         base = 1)

Arguments

• n: a (possibly named) vector of sample sizes for each group.
• type: type of contrast.
• base: an integer specifying which group is considered the baseline group for Dunnett contrasts.

Details

Computes the requested matrix of contrasts for comparisons of mean levels.

Returns

The matrix of contrasts with appropriate row names is returned.

References

Frank Bretz, Torsten Hothorn and Peter Westfall (2010), Multiple Comparisons Using R, CRC Press, Boca Raton.

Frank Bretz, Alan Genz and Ludwig A. Hothorn (2001), On the numerical availability of multiple comparison procedures. Biometrical Journal, 43 (5), 645--656.

Examples

n <- c(10,20,30,40)
 names(n) <- paste("group", 1:4, sep="")
 contrMat(n)    # Dunnett is default
 contrMat(n, base = 2)  # use second level as baseline
 contrMat(n, type = "Tukey")
 contrMat(n, type = "Sequen")
 contrMat(n, type = "AVE")
 contrMat(n, type = "Changepoint")
 contrMat(n, type = "Williams")
 contrMat(n, type = "Marcus")
 contrMat(n, type = "McDermott")
 ### Umbrella-protected Williams contrasts, i.e. a sequence of 
 ### Williams-type contrasts with groups of higher order 
 ### stepwise omitted
 contrMat(n, type = "UmbrellaWilliams")
 ### comparison of each group with grand mean of all groups
 contrMat(n, type = "GrandMean")