Terminal digit preference in blood pressure measurements: effects on epidemiological associations

A study was conducted to determine the extent of terminal digit preference in recording blood pressures in an industrial screening programme and its effect on the estimates of the associations between blood pressure and both age and body mass index (BMI). The results showed that 78.5% of systolic and 74.2% of diastolic blood pressure readings were digit preferenced (p less than 0.0001) and that the examining doctors were least likely to preference their readings near the diagnostically important cut-off points of 150 mmHg systolic and 90 mmHg diastolic. Digit preferencing did not generally affect estimates of the slopes and intercepts of the relationships between blood pressure and age or BMI, however, the associations between blood pressure and both age and BMI showed greater error variance when digit preferenced readings were used compared to non-digit preferenced readings. Digit preferencing would have the effect of reducing the power of statistical tests thereby making it more difficult to assess associations between blood pressure and other potential risk factors.