J Martin Bland, professor of health statistics , Douglas G Altman, professor of statistics in medicine. Department of Health Sciences, University of York, York YO10 5DD, 2 Centre for Statistics in Medicine, University of Oxford, Wolfson College Annexe, Oxford OX2 6UD
Studies with small numbers of measurements are rare in the modern BMJ, but they used to be common and remain plentiful in specialist clinical journals. Their analysis is often more problematic than that for large samples.