Twenty percent of adults in Canada are hypertensive according to the Canada Health Surveys conducted between 1986 and 1992.  This constitutes about 4.3 million people. These numbers are similar to other countries where similar population surveys have been done  : France 22.1%, UK 37.8%, USA 20.1%. While it is lower than reported in other countries  : Spain 68.3% and Tawain 42%.
Of the 4.3 million adults in Canada with hypertension, 57% are aware of the diagnosis, 34% are being treated, and 13% are treated and controlled. Therefore, of the 1,426,000 being treated, only 559,000(39%) have achieved target (<140/90) and 867,000 (61%) are not under adequate control . These estimates of blood pressure control are similar to those reported in France and Spain, better than the UK, but not as good as those reported in the USA. He et al  recently calculated that poor blood pressure control was responsible for 62,000 unnecessary deaths each year in the UK.
Hypertension is an important risk factor for all major atherosclerotic cardiovascular disease outcomes, including cardiac failure, stroke, coronary artery disease, and peripheral vascular disease . So why are we doing so poorly? Are the results any better if we look at clinical practice information rather than population data? In 2001 Seddon  conducted a systematic review of studies of quality of clinical care in general practice in the UK, Australia, and New Zealand. In the 11 papers related to care of hypertension in clinical practice, 51–64% of people with hypertension were being treated and of those being treated between 31 and 83% were controlled according to guidelines.
However it is important to consider the degree of "lack of control". In 2003, Amar  in a study of patients with hypertension and coronary disease found that while as many as 67% of patients were uncontrolled, over half of these were categorized as such because of borderline systolic blood pressure; their diastolic blood pressures were normal. Elevated systolic blood pressures were not treated as rigorously as elevated diastolic blood pressures.
In this paper we report the degree to which systolic vs diastolic blood pressure contribute to a determination of inadequate blood pressure control in family physicians' practices, and the accuracy of that determination when compared to the results of 24 hour ambulatory monitoring. An underlying hypothesis is that white coat effect is partially responsible for the reported low rates of control of hypertension by primary care practitioners.