Litter Weights Data Set

Description

Dose response of litter weights in rats; data set taken from Westfall et al. (1999, p. 109). Specific dose comparisons in a dose response experiment with two covariates.

Usage

data(litter)

Format

This data frame contains the following variables

dose

Dosages at 4 levels: 0, 5, 50, 500.

gesttime

Gestation time as covariate.

number

Number of animals in litter as covariate.

weight

Response variable: average post-birth weights in the entire litter.

Details

See Westfall et al. (1999, p. 109)

Source

P. H. Westfall, R. D. Tobias, D. Rom, R. D. Wolfinger, Y. Hochberg (1999). Multiple Comparisons and Multiple Tests Using the SAS System. Cary, NC: SAS Institute Inc.

Examples

data(litter)

# define the contrast matrix, either completly
C <- matrix(c(0,0,0,0,0,0,1,1,1,.75,.384,.887,-1,0,0,.25,.37,.113,
       0,-1,0,-.25,.246,-.339,0,0,-1,-.75,-1,-.661,0,0,0,
       0,0,0,0,0,0,0,0,0), ncol=7)
# numerate the contrasts
rownames(C) <- paste("C", 1:nrow(C), sep="")

# simultaneous confidence intervals for above comparisons 
# in an ANCOVA
summary(simint(weight ~ dose + gesttime + number, data=litter,
               alternative="greater", cmatrix=C))

# or for dose only
D <- matrix(c(1,1,1,.75,.384,.887,-1,0,0,.25,.37,.113,0,-1,0,-.25,
              .246,-.339,0,0,-1,-.75,-1,-.661),ncol = 4)
rownames(D) <- paste("D", 1:nrow(D), sep="")

summary(simint(weight ~ dose + gesttime + number, data=litter,
               whichf="dose", alternative="greater", cmatrix=D))