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Statistics notes Variables and parameters

BMJ 1999; 318 doi: (Published 19 June 1999) Cite this as: BMJ 1999;318:1667
  1. Douglas G Altman, professor of statistics in medicinea,
  2. J Martin Bland, professor of medical statisticsb
  1. aICRF Medical Statistics Group, Centre for Statistics in Medicine, Institute of Health Sciences, Oxford OX3 7LF
  2. b Department of Public Health Sciences, St George's Hospital Medical School, London SW17 0RE
  1. Correspondence to: Professor Altman

    Like all specialist areas, statistics has developed its own language. As we have noted before,1 much confusion may arise when a word in common use is also given a technical meaning. Statistics abounds in such terms, including normal, random, variance, significant, etc. Two commonly confused terms are variable and parameter; here we explain and contrast them.

    Information recorded about a sample of individuals (often patients) comprises measurements such as blood pressure, age, or weight and attributes such as blood group, stage of disease, and diabetes. Values of these will vary among the subjects; in this context blood pressure, weight, blood group and so on are variables. Variables are quantities which vary from individual to individual.

    By contrast, parameters do not relate to …

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