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General Practice

Statistics notes: Cronbach's alpha

BMJ 1997; 314 doi: (Published 22 February 1997) Cite this as: BMJ 1997;314:572
  1. J Martin Bland, professor of medical statisticsa,
  2. Douglas G Altman, headb
  1. a Department of Public Health Sciences St George's Hospital Medical School London SW17 0RE
  2. b ICRF Medical Statistics Group Centre for Statistics in Medicine Institute of Health Sciences PO Box 777 Oxford OX3 7LF
  1. Correspondence to: Professor Bland


    Many quantities of interest in medicine, such as anxiety or degree of handicap, are impossible to measure explicitly. Instead, we ask a series of questions and combine the answers into a single numerical value. Often this is done by simply adding a score from each answer. For example, the mini-HAQ is a measure of impairment developed for patients with cervical myelopathy.1 This has 10 items (table 1)) recording the degree of difficulty experienced in carrying out daily activities. Each item is scored from 1 (no difficulty) to 4 (can't do). The scores on the 10 items are summed to give the mini-HAQ score.

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    Table 1

    Mini-HAQ scale in 249 severely impaired subjects

    When items are used to form a scale they need to have internal consistency. The …

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