A veterinarian is studying three different medications that could be used in the prevention of heartworm in young puppies. She has acquired for study four different litters of cocker spaniels, and three puppies were randomly selected from each litter. The three selected puppies from a litter were then randomly assigned to one of the three treatments. The data below represents the number of months after a single treatment before the initial onset of heartworm in the puppies. Is there sufficient evidence that the mean time to onset of heartworm differs among the three different medications