Data and safety monitoring board: A committe set up to monitor a clinical trial for patient safety and for evidence of benefit. Needed to ensure minimal acceptable risks to trial participants and to continually reassess the risks versus benefits of trial interventions. [Circulation, 1995, 91, 901–4].

Data archives: Generally large sets of data that can be accessed and utilized by researchers intending to perform secondary data analysis. Such archives preserve important data against disposal or deterioration. [British Medical Journal, 1994, 308, 1519–20.]

Database: A structured collection of data that is organized in such a way that it may be accessed easily by a wide variety of applications programs. Large clinical databases are becoming increasingly available to clinical and policy researchers and are generally used for two purposes: to facilitate healthcare delivery and for research. An example of such a database is that provided by the US Health Care Financing Administration, which contains information about all Medicare patients' hospitalizations, surgical procedures and surgery visits. See also administrative databases. [Elmasri, R. and Navathe, S. B., 1994, Fundamentals of Database Systems, 2nd edn, Addison-Wesley, Reading, MA.]

Database management system: A computer system organized for the systematic management of a large, structured collection of information that can be used for storage, modification and retrieval of data. [Controlled Clinical Trials, 1995, 16, 30S–65S.]

Data dredging: A term used to describe comparisons made withing a data set not specifically described before the start of the study. [Altman, D. G., 1991, Practical Statistics for Medical Research, CRC/Chapman & Hall, London.]