heplots (version 1.0-2)

WeightLoss: Weight Loss Data

Description

Contrived data on weight loss and self esteem over three months, for three groups of individuals: Control, Diet and Diet + Exercise. The data constitute a double-multivariate design.

Usage

data(WeightLoss)

source

Originally taken from http://www.csun.edu/~ata20315/psy524/main.htm, but modified slightly

Details

Helmert contrasts are assigned to group, comparing Control vs. (Diet DietEx) and Diet vs. DietEx.

References

Friendly, Michael (2010). HE Plots for Repeated Measures Designs. Journal of Statistical Software, 37(4), 1-40. URL http://www.jstatsoft.org/v37/i04/.

Examples

data(WeightLoss)
str(WeightLoss)
table(WeightLoss$group)

contrasts(WeightLoss$group) <- matrix(c(-2,1,1, 0, -1, 1),ncol=2)
(wl.mod<-lm(cbind(wl1,wl2,wl3,se1,se2,se3)~group, data=WeightLoss))

heplot(wl.mod, hypotheses=c("group1", "group2"))
pairs(wl.mod, variables=1:3)
pairs(wl.mod, variables=4:6)

# within-S variables
within <- data.frame(measure=rep(c("Weight loss", "Self esteem"),each=3), month=rep(ordered(1:3),2))

# doubly-multivariate analysis: requires car 2.0+
if (packageDescription("car")[["Version"]] >= 2) {
imatrix <- matrix(c(
	1,0,-1, 1, 0, 0,
	1,0, 0,-2, 0, 0,
	1,0, 1, 1, 0, 0,
	0,1, 0, 0,-1, 1,
	0,1, 0, 0, 0,-2,
	0,1, 0, 0, 1, 1), 6, 6, byrow=TRUE)
# NB: for heplots the columns of imatrix should have names
colnames(imatrix) <- c("WL", "SE", "WL.L", "WL.Q", "SE.L", "SE.Q")
rownames(imatrix) <- colnames(WeightLoss)[-1]
(imatrix <- list(measure=imatrix[,1:2], month=imatrix[,3:6]))
contrasts(WeightLoss$group) <- matrix(c(-2,1,1, 0,-1,1), ncol=2) 
(wl.mod<-lm(cbind(wl1, wl2, wl3, se1, se2, se3)~group, data=WeightLoss))
(wl.aov <- Anova(wl.mod, imatrix=imatrix, test="Roy"))

heplot(wl.mod, imatrix=imatrix, iterm="group:measure")
}

# do the correct analysis 'manually'
unit <- function(n, prefix="") {
	J <-matrix(rep(1, n), ncol=1)
	rownames(J) <- paste(prefix, 1:n, sep="")
	J
}                

measure <- kronecker(diag(2), unit(3, 'M')/3, make.dimnames=TRUE)
colnames(measure)<- c('WL', 'SE')

between <- as.matrix(WeightLoss[,-1])
between.mod <- lm(between ~ group, data=WeightLoss)
Anova(between.mod)

heplot(between.mod, hypotheses=c("group1", "group2"), 
	xlab="Weight Loss", ylab="Self Esteem",
	col=c("red", "blue", "brown"),
	main="Weight Loss & Self Esteem: Group Effect")

month <- kronecker(diag(2), poly(1:3), make.dimnames=TRUE)
colnames(month)<- c('WL', 'SE')
trends <- as.matrix(WeightLoss[,-1])within.mod <- lm(trends ~ group, data=WeightLoss)
Anova(within.mod)

heplot(within.mod)
heplot(within.mod, hypotheses=c("group1", "group2"), 
	xlab="Weight Loss", ylab="Self Esteem",
	type="III", remove.intercept=FALSE,
	term.labels=c("month", "group:month"),
	main="Weight Loss & Self Esteem: Within-S Effects")
mark.H0()