Several observational studies have suggested that owning pets may have a positive effect on both physical and mental health. However, to date there have not been any large scale experimental studies.

a)[2 marks]Explain why it might be difficult to assess a cause and effect relationship based on the observational studies.

b)[2 marks]If you were to assess the benefit of pet ownership via a controlled trial, how should the people taking part in the controlled trials be selected? How should they be allocated to the control or treatment group?

c)[3 marks]In a double-blind experiment neither the participants or the people taking measurements know who is receiving the treatment or control. Why is this considered important? Would it be possible to do. a double-blind experiment in this case?