Appearance ratings of washed and unwashed panels
A data frame with 36 observations on the following 3 variables.
type of treatment - a factor with levels
NW (not washed) and
rating after 2 weeks
A particular durability test of paint involves applying drops of acid on the panel. After a particular time point the panel is rated for its ability to withstand the acid. This study involved washing (or not washing) panels and then storing them for two weeks to see if there was a residual effect of the acid on the panel. This was important as panels are often stored and used in presentations so the researchers needed to know if they should wash the panels before storing them.
Peter R. Nelson, Marie Coffin and Karen A. F. Copeland (2003), Introductory Statistics for Engineering Experimentation, Elsevier. (Appendix A)
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str(wash) summary(wash) show(plt1 <- xyplot(time2 ~ time1, wash, groups = type, auto.key = list(columns = 2, lines = TRUE), aspect = "iso", type = c("g","p","smooth"), xlab = "Initial rating", ylab = "Rating after 2 weeks", jitter.x = TRUE, jitter.y = TRUE)) tmd(plt1) densityplot(~ I(time2 - time1), wash, groups = type, auto.key = list(columns = 2, lines = TRUE), xlab = "Change in rating after two weeks")
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