Turbidity of a toothpaste formulation
Results from an experiment to assess the turbidity of a toothpaste formulation. The three factors that are varied at the NaCl level, the reaction temperature and the addition rate of a particular component.
A data frame with 8 observations on the following 4 variables.
NaClNaCl level (2 or 20 ml.)
tempReaction temperature (50 or 80 degrees C)
rateAddition rate (30 or 60 seconds)
turbiditya numeric vector
Peter R. Nelson, Marie Coffin and Karen A. F. Copeland (2003), Introductory Statistics for Engineering Experimentation, Elsevier. (Appendix A)
str(tpaste)
opt <- options(contrasts = c("contr.treatment", "contr.helmert"))
summary(fm6 <- lm(turbidity ~ (NaCl + temp + rate)^3, tpaste))$coefficients
qqmath(coef(fm6)[-1], xlab = "Standard normal quantiles",
ylab = "Estimated coefficients", aspect = 1, type = c("g", "p"),
panel = function(...){panel.qqmath(...); panel.qqmathline(...,lty=2,alpha=0.5)})
xyplot(sort(abs(coef(fm6)[-1])) ~ sqrt(qchisq(ppoints(7), df = 1)),
xlab = "Quantiles of absolute value of the standard normal",
ylab = "Absolute value of estimated coefficients", type = c("g","p"))
summary(fm7 <- lm(turbidity ~ NaCl * rate, tpaste))
options(opt)Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.