Fiber data
Fiber data from Montgomery Design (8th ed.), p.656 (Table 15.10). Useful as a simple analysis-of-covariance example.
fiber
A data frame with 15 observations and 3 variables:
machinea factor with levels A B C.
This is the primary factor of interest.
strengtha numeric vector. The response variable.
diametera numeric vector. A covariate.
The goal of the experiment is to compare the mean breaking strength of fibers produced by the three machines. When testing this, the technician also measured the diameter of each fiber, and this measurement may be used as a concomitant variable to improve precision of the estimates.
Montgomery, D. C. (2013) Design and Analysis of Experiments (8th ed.). John Wiley and Sons, ISBN 978-1-118-14692-7.
fiber.lm <- lm(strength ~ diameter + machine, data=fiber) ref_grid(fiber.lm) # Covariate-adjusted means and comparisons emmeans(fiber.lm, pairwise ~ machine)
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