Cross-cultural validation of the Hill-Bone compliance to high blood pressure therapy scale in a South African, primary health care setting

In Black South Africans, hypertension (≤=160/95 mmHg) (HTN) is prevalent (14.1% of men and 15.7% of women), under-diagnosed, inadequately treated, and little studied. Prior to conducting a clinical trial to improve HTN control in Black South Africans, we validated the Hill-Bone Compliance Scale which has demonstrated predictive validity in young urban Black American males with HTN. Black, hypertensive patients (N=98) were recruited from primary health care clinics in metropolitan Cape Town. The questionnaire was translated into Xhosa, the first language of the subjects, back-translated into English, and adapted to the local context and vernacular. Weight, height and BP (using the Omron electronic monometer after 5 min of seated rest) were measured. Mean BP was 150/94 mmHg. Item analysis was conducted to determine internal consistency of the Scale and the 9-item medication subscale. Spearman's rank order correlations were used to assess the relationship between compliance scores and BP. The subscale demonstrated good internal consistency with item-total correlations all exceeding 0.32, and a standardized Cronbach's alpha of 0.75, with an average inter-item correlation of 0.26. The subscale had significant predictive validity in that non-compliance predicted higher systolic blood pressures (rho = 0.24, P < 0.03 for total scale and rho = 0.20, P < 0.04 for subscale). These analyses provide evidence of criterion validity and internal consistency for the Hill-Bone Compliance to High Blood Pressure Therapy Scale, in black, urban hypertensives living in Cape Town. These results compare favourably with those from an urban African-American setting.