An authors’ error occurred in this article by Dr Jones and others (2003;20:453–8)

We wish to clarify the following points in relation to the section on diagnostic sample size calculations.

(1) The method described is used to calculate the sample size required to estimate an expected level of sensitivity or specificity with a predefined degree of precision. If the researcher wishes to ensure that a particular test has a sensitivity or specificity higher than a predetermined level then an alternative method should be used.¹

(2) The language used in the section on diagnostic tests may be misleading. The method described should use “expected” levels of sensitivity or specificity (SN or SP) to calculate the sample size, rather than the “lowest acceptable” level.

(3) The method described should not be used if there are fewer than five subjects in any of the cells of the 2×2 table.

We would like to sincerely thank Steve Goodacre for his assistance in recognising the problem and for his assistance in resolving it.