BMJ 2001;323:1123-1124

Andrew J Vickers, assistant attending research methodologist a, Douglas G Altman, professor of statistics in medicine b.

a Integrative Medicine Service, Biostatistics Service, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA, b ICRF Medical Statistics Group, Centre for Statistics in Medicine, Institute of Health Sciences, Oxford
In many randomised trials researchers measure a continuous variable at baseline and again as an outcome assessed at follow up. Baseline measurements are common in trials of chronic conditions where researchers want to see whether a treatment can reduce pre-existing levels of pain, anxiety, hypertension, and the like.