Jacobsen et al. (2002) sent nine "identical" soil samples to eight soil testing laboratories in the Great Plains region of the Central United States over a three year period of time. Among other characteristics the labs were paid to measure soil potassium. A question of interest was whether the labs would produce identical analytical results.
data(K)
A data frame with 72 observations on the following 2 variables.
K
Soil K in mg/kg
lab
Laboratories, a factor with levels B
D
E
F
G
H
I
J