End-digit preference in blood pressure recordings of patients with ischaemic heart disease in primary care.
End-digit preference describes the disproportionate selection of specific end digits. The rounding of figures might lead to either an under- or over-recording of blood pressure (BP) and a lack of accuracy and reliability in treatment decisions. A total of 85 000 BP values taken from computerised general practice records of ischaemic heart disease patients in England between 2001 and 2003 were examined. Zero preference accounts for 64% of systolic and 59% of diastolic readings, compared with an expected frequency of 10% (P<0.000001). Even numbers are more frequently seen than odd numbers. In all, 64% of nonzero systolic recordings and 65% of diastolic recordings ended in even numbers, compared with expected proportions of 44% (P<0.0001). Among the nonzero even numbers, eight is the most frequently observed: 28% of systolic and 31% of diastolic recordings compared with an expected proportion of 25% (P<0.0001). Among the five nonzero odd numbers, five is the most frequently observed end digit, representing 59% systolic and 62% of diastolic compared with an expected level of 20% (P<0.00001). English general practice displays marked end-digit preference. This is strongly for the end-digit zero. However, there is more use of other end-digits, notably 8 and 5. This bias potentially carries important treatment consequences for this high-risk population.
de Lusignan
S
S
Primary Care Informatics, Department of Community Health Sciences, St George's Hospital Medical School, London, UK. slusigna@sghms.ac.uk
Belsey
J
J
Hague
N
N
Dzregah
B
B
D001794:Blood Pressure / Q000502:physiology*; D001795:Blood Pressure Determination; D003971:Diastole / Q000502:physiology; D004739:England / Q000453:epidemiology; D006801:Humans; D017202:Myocardial Ischemia / Q000453:epidemiology / Q000503:physiopathology*; D015588:Observer Variation; D011320:Primary Health Care; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted; D013599:Systole / Q000502:physiology