# The response is the length of odontoblasts (teeth) in each of 10 guinea pigs
# at each of three dose levels of Vitamin C (0.5, 1, and 2 mg) with each of two
# delivery methods (orange juice or ascorbic acid).
#
#
#  Format:
#     A data frame with 60 observations on 3 variables.
#       [,1]  len   numeric  Tooth length                
#       [,2]  supp  factor   Supplement type (VC or OJ). 
#       [,3]  dose  numeric  Dose in milligrams.         
#
# Plot the data with len as the response. Fit a linear model to the data and
# check for possible simplification. Display the fitted regression lines on top
# of the data

"len" "supp" "dose"
"1" 4.2 "VC" 0.5
"2" 11.5 "VC" 0.5
"3" 7.3 "VC" 0.5
"4" 5.8 "VC" 0.5
"5" 6.4 "VC" 0.5
"6" 10 "VC" 0.5
"7" 11.2 "VC" 0.5
"8" 11.2 "VC" 0.5
"9" 5.2 "VC" 0.5
"10" 7 "VC" 0.5
"11" 16.5 "VC" 1
"12" 16.5 "VC" 1
"13" 15.2 "VC" 1
"14" 17.3 "VC" 1
"15" 22.5 "VC" 1
"16" 17.3 "VC" 1
"17" 13.6 "VC" 1
"18" 14.5 "VC" 1
"19" 18.8 "VC" 1
"20" 15.5 "VC" 1
"21" 23.6 "VC" 2
"22" 18.5 "VC" 2
"23" 33.9 "VC" 2
"24" 25.5 "VC" 2
"25" 26.4 "VC" 2
"26" 32.5 "VC" 2
"27" 26.7 "VC" 2
"28" 21.5 "VC" 2
"29" 23.3 "VC" 2
"30" 29.5 "VC" 2
"31" 15.2 "OJ" 0.5
"32" 21.5 "OJ" 0.5
"33" 17.6 "OJ" 0.5
"34" 9.7 "OJ" 0.5
"35" 14.5 "OJ" 0.5
"36" 10 "OJ" 0.5
"37" 8.2 "OJ" 0.5
"38" 9.4 "OJ" 0.5
"39" 16.5 "OJ" 0.5
"40" 9.7 "OJ" 0.5
"41" 19.7 "OJ" 1
"42" 23.3 "OJ" 1
"43" 23.6 "OJ" 1
"44" 26.4 "OJ" 1
"45" 20 "OJ" 1
"46" 25.2 "OJ" 1
"47" 25.8 "OJ" 1
"48" 21.2 "OJ" 1
"49" 14.5 "OJ" 1
"50" 27.3 "OJ" 1
"51" 25.5 "OJ" 2
"52" 26.4 "OJ" 2
"53" 22.4 "OJ" 2
"54" 24.5 "OJ" 2
"55" 24.8 "OJ" 2
"56" 30.9 "OJ" 2
"57" 26.4 "OJ" 2
"58" 27.3 "OJ" 2
"59" 29.4 "OJ" 2
"60" 23 "OJ" 2