First, the researchers measured ambulatory blood pressure [the blood pressure outside the doctor's office] in the 295 people with normal office blood pressures. To do this, they had the people wear portable blood pressure monitors. These are small machines that measure and record blood pressure as people go about their usual activities. They found that 61 of these people had high ambulatory blood pressure even though they had normal blood pressure in their doctors' offices. This left them with three groups.: 1) people who had normal blood pressure in and out of doctors' offices, 2) people who had white coat normotension, and 3) people who had high blood pressure both in and out of doctors' offices.