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.
KSoil K in mg/kg
labLaboratories, a factor with levels B D E F G H I J