A doctor has conditioned heart rate in two strains of rats. One third of the animals were injected with saline before conditioning, one third with 0.5 mg/kg of atropine, and one third with 10 mg/kg atropine. Fifteen animals were randomly selected from each strain and five were randomly assigned to each drug condition. Heart rate changes were recorded. These data are shown below :

Heart Rate Changes Omg 5mg 10mg Strain 1 1,2,3,2,4 8,7,9,9,5 9,8,7,10,9 Strain 2 0,1,2,1,0 5,6,7,5,5 6,7,8,8,5