Have you heard of “pet therapy”? Access to a pet (typically, but not limited to, a dog) has been shown to be associated with beneficial physical responses like lowered blood pressure and reduced...

Have you heard of “pet therapy”?  Access to a pet (typically, but not limited to, a dog) has been shown to be associated with beneficial physical responses like lowered blood pressure and reduced anxiety.  In a review of the pet therapy literature, Giaquinto and Vlanetini (2009) describe a study that compared two groups of heart patients.  Group 1 consisted of patients with high blood pressure and who owned pets.  These participants were matched with participants in a control group who also had high blood pressure but did not own pets.  Six months later, blood pressure was measured in both groups.  Does having a pet reduce blood pressure?

what statistical test should be used and why?