tpaste {EngrExpt}

Turbidity of a toothpaste formulation

Description

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.

Format

A data frame with 8 observations on the following 4 variables.

NaCl

NaCl level (2 or 20 ml.)

temp

Reaction temperature (50 or 80 degrees C)

rate

Addition rate (30 or 60 seconds)

turbidity

a numeric vector

References

Peter R. Nelson, Marie Coffin and Karen A. F. Copeland (2003), Introductory Statistics for Engineering Experimentation, Elsevier. (Appendix A)

Examples

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)