Fiber data

Description

Fiber data from Montgomery Design (8th ed.), p.656 (Table 15.10). Useful as a simple analysis-of-covariance example.

Usage

fiber

Format

A data frame with 15 observations on the following 3 variables.

machine

a factor with levels A B C. The primary factor of interest.

strength

a numeric vector. The response variable.

diameter

a numeric vector. A covariate.

Details

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.

Source

Montgomery, D. C. (2013) Design and Analysis of Experiments (8th ed.). John Wiley and Sons, ISBN 978-1-118-14692-7.

Examples

require(lsmeans)
fiber.lm <- lm(strength ~ diameter + machine, data=fiber)
ref.grid(fiber.lm)

# Covariate-adjusted means and comparisons
lsmeans(fiber.lm, pairwise ~ machine)