How many measurements should be averaged?
As is the case with ambulatory blood pressure [15–18], the reproducibility of home blood pressure is clearly dependent on the number of measurements that are averaged [19]. Chatellier et al. [19] showed that the maximal reproducibility of home blood pressure (reduction in the standard deviation of differences between the average values of two home blood pressure sessions) is obtained when 30 readings are averaged (three measurements per day for 10 consecutive days). Eighty per cent of this maximal reduction is, however, obtained by averaging 15 measurements on the first 5 days. On the other hand, Imai et al. [20], although confirming that the reproducibility of home blood pressure is at least partly dependent on the number of measurements, provided evidence that no further improvement is obtained by increasing the number of home blood pressure readings above five. This conclusion is in agreement with the results of the SMART study [21], which also showed that, after only six home blood
