The participants (n ¼50), aged 40 to 71, were diagnosed
essential arterial hypertension patients of San Jos e health centre in
Las Palmas de Gran Canaria. They were randomly selected from a
list which had been created, also randomly, by the team of physicians of the health centre. 25 patients were assigned to each group
(study group and control group) by systematic random sampling.
After appointments with each of these initial participants, they
were randomly selected from the list until the consent of participation in the study was obtained from 20 patients in each group.