The impact of observer and patient factors on the occurrence of digit preference for zero in blood pressure measurement in a hypertension specialty clinic: Evidence for the need of continued observation

Background: Many investigators have reported unconscious over-reporting of the terminal digit zero but little literature exists on observer or patient-related factors that may predict the occurrence. This study analyzes the occurrence of zero preference in 52,827 blood pressure (BP) measurements in 8513 patients by 11 hypertension nurse specialists in the Hypertension Division at Mayo Clinic, Rochester, Minnesota. Methods: Data from the electronic database of the Hypertension Division from April 1997 to September 2001 were analyzed for the occurrence of zero preference. Nurse-specific zero preference was stratified on four variables: number of BPs performed, years as hypertension nurse specialist, time of day BP performed (fatigue), and nursing degree. Three patient-specific factors were analyzed: age at visit (stratified by decade), type of care (continuing versus short-term), and hypertension status. Results: We found significantly increased frequency of zero preference for all BPs with mean frequency of 31% v 20% expected (P <.0001). Individual nurse zero preference varied widely, 22.0% to 53.6% for systolic BP and 22.2% to 40.8% for diastolic BP). Continuing care patients had a higher zero preference than did short-term care patients for both systolic BP (34.5% v 30.2%; P <.0001) and diastolic BP (34.7% 1, 33.3%; P =.006). Zero preference was also more common at hi-her categories of hypertension (P <.001). Time of day, nursing degree, patient age, the number of BPs performed, years of service did not affect the occurrence of digit preference. Conclusions: Digit preference was demonstrated and varied significantly among well-trained hypertension nurse specialists. Further studies in a larger number of observers are required.