Bulls can develop respiratory issues as they get older. This may compromise their ability to breath properly which affects their energy level and overall health. A researcher wishes to conduct a study to find which of two injection therapies, Therapy A or Therapy B, is more effective in improving respiratory health. A total of 180 bulls that are at least 12 years old will be randomly selected from ranches in the state of Texas. The researcher will get consent from all owners, treat the bulls for eight months and evaluate changes in respiratory health. Part A: How would the study benefit from adding a control group?
Part B: What is the best way to randomly place the bulls into the Therapy A, Therapy B, and control groups?
Part C: The researcher wants to use a blocking variable to place the bulls into groups instead of doing it randomly. He decides to block either by breed or ranch. Explain which would be the best blocking method.