Intended for healthcare professionals

Research Methods & Reporting Statistics Notes

Brackets (parentheses) in formulas

BMJ 2011; 343 doi: (Published 11 August 2011) Cite this as: BMJ 2011;343:d570

And another thing

Dear Sir,

We were interested to see Douglas Altmann's piece on arithmetical
brackets. Everyone over 50 will recognise it as the B of BODMAS. The lack
of arithmetical competence may reflect the fact that BODMAS is not taught
in primary schools in the 21st century, meaning many young doctors are
not able to sort out the hierarchy of multiplication before addition.

Another arithmetical operation that is a common cause of confusion is
the decimal point, although we have not yet seen anyone blame this lack of
facility on the teaching of Imperial Measure preceding decimalisation in
Feb 1971.

Small babies need small doses. Everyone 'knows that'. A 3 kg sick
little baby could usefully have an intravenous dose of 30 microgrammes of
morphine. The difficulty is that this is not 0.3 mls of a standard ampoule
but a tiny 0.03 mls which can be construed as unlikely or impossible. In
goes the ten-times overdose, which is the greater mistake.

The problem is not new. One of us reported (1) in 1995 that doctors'
arithmetical precision was disappointingly poor as measured by a
straightforward questionnaire of drugs commonly used in medical

In 2011, we find that little has changed other than, this time, a
professor of statistics has confirmed that doctors cannot do sums. Papers
are written and published on the subject but incorrect doses continue to
be given and doctors continue to be suspended from practice.

Sian Rolfe FRCA,

Oliver Dearlove FRCA

1. Rolfe S, Harper NJN. Ability of hospital doctors to calculate
drug doses. BMJ 1995;310:1173-4.

Competing interests: No competing interests

04 October 2011
Oliver Dearlove
Sian Rolfe
Royal Manchester Children's Hospital