A clinical trial was conducted by veterinarians specializing in feline internal medicine to determine the efficacy of a drug therapy for the treatment of erythrocytosis in cats. Erythrocytosis (or polycythemia) is defined by the increase in total red blood cells and is diagnosed through a complete blood cell count (CBC) test. The disease can be classified as either primary or secondary. A total of 40 cats were enrolled in the study. Half of these cats had previously been diagnosed with primary erythrocytosis (Type = 1) and the other half had been diagnosed with secondary erythrocytosis (Type=0). The cats belong to one of 5 breeds (Breed); breeds A, B, and C are classified as domestic (Domestic = 1) and breeds D and E are classified as non-domestic (Domestic = 0). Each cat was given a specific dose (Dose) of the drug hydroxyurea for a period of 3 months. The veterinarians recorded the change in packed cell volume (PCV)following treatment (the more negative, the better). The data is available on Carmen in the file cats.txt. You can read in the data with the following code in R:

Delta PCV Type Dose Breed -5.4 0 2 A -4.8 1 6 A -6.5 1 7 A -7.8 0 9 A -8.3 0 9 A -7.2 1 6 A -5.5 0 7 B -5.5 1 8 B -5.7 1 9 B -5.8 0 8 B -3.7 1 5 B -6.2 0 7 B -4.9 1 5 B -3.3 0 3 B -7 0 3 C -6.2 0 8 C -5.3 0 2 C -5.7 0 3 C -3.7 1 2 C -6.2 1 5 C -4.7 0 2 C -5.5 0 4 C -6.3 1 6 C -6.8 0 6 C -1.5 1 3 D -4.9 0 9 D -2.6 1 5 D 0.2 0 3 D -3.6 1 5 D -3.1 0 2 D -3.3 0 7 E -3.8 0 6 E -4.2 1 9 E -4.1 1 4 E -4 1 4 E -2 1 4 E -5.3 1 7 E -6.4 1 8 E -5.2 0 8 E -3.1 1 4 E

# read in the data catsData <- read.table("cats.txt", header=T ) y <- catsData$DeltaPCV breed <- as.numeric(factor(catsData$Breed)) domestic <- c(1,1,1,0,0) nBreeds <- 5 nCats <- length(y)