The Observer Variation in the Measurement of Arterial Blood Pressure

Observer errors and observer variation have been studied in a survey of blood pressure covering about 70,000 subjects in Bergen, Norway, carried out by 19 specially trained nurses under conditions standardized as much as possible. Substantial differences were found between extreme observers concerning the mean values of the readings in age and sex groups, while the majority only showed insignificant differences. Reading characteristics were supposed to be the reason for individual observers keeping the same ranking position vis‐à‐vis the others from age group to age group in both sexes. A number of observers had, however, a different ranking in systolic from that in diastolic readings. Terminal digit preference in the readings was found only to a small degree, and only in a few of the observers. The special apparatus of the London School of Hygiene was found to reduce, but not to eliminate this error. When the results obtained with the latter apparatus were compared to standard apparatus results, no differences in the reading characteristics were found related to the sex, age and blood pressure level of the subjects examined. Conclusion: observer variation in blood pressure examination may be substantial and may affect the mean values found in population surveys, even if the observers are carefully selected and thoroughly trained.