Further reading
- Abramson, J H (1984). Survey Methods in Community Medicine. Third edition. New York: Churchill Livingston.
- Lowe, D (1993). Planning for Medical Research: a Practical Guide to Research Methods. First edition. Middlesborough: Astraglobe.
- Seigel, S and Castallan, N J (1988). Nonparametric Statistics for the Behavioural Sciences. Second edition. New York: McGraw-Hill.
- Streiner, D L and Norman, G R (1994). Health Measurement Scales. A Practical Guide to their Use and Development. Oxford: Oxford University Press.