The Journal of Clinical Pathology publishes about nine papers a month presenting comparative (mostly primary) data. Their aim is to inform the clinical readership about the effects of disease or the comparative effectiveness of differing treatments.

During the last 10 years many internationally recognised reporting guidelines within health research have been developed. The most notable of these are CONSORT (CONsolidated Standards Of Reporting Trials1), STROBE (STrengthening the Reporting of Observational studies in Epidemiology2) and STARD (STAndards for the Reporting of Diagnostic accuracy studies3). However, these guidelines have been used infrequently. Last year the umbrella network EQUATOR (Enhancing the QUAlity and Transparency Of health Research4) was officially launched with the aim of enhancing the reliability of medical research literature by promoting transparent and accurate reporting of research results. One way the network aimed to do this was by increasing the usage of robust reporting guidelines such as CONSORT, STROBE and STARD. The J Clin Pathol supports this initiative, and the EQUATOR network is cited within the author instructions.

All the guidelines require that estimates should be given with some measure of precision that is dependent on the sample size. This precision usually takes the form of a confidence interval around the point estimate of effect. A review of the 3 months April to June 2009 revealed that of 28 J Clin Pathol articles presenting sample data, only six mentioned confidence intervals, and only four presented them correctly for all relevant estimates. To facilitate adherence to the current guidelines for contributors to J Clin Pathol, this paper gives an overview of confidence intervals and their interpretation in the most commonly encountered data scenarios. We do not give details of calculation as this can be done by any good statistics package, and the researcher does not need to …