Standard Article

Coefficient Alpha

  1. Jeffrey T. Steedle1,
  2. Richard J. Shavelson2

Published Online: 30 JAN 2010

DOI: 10.1002/9780470479216.corpsy0190

Corsini Encyclopedia of Psychology

Corsini Encyclopedia of Psychology

How to Cite

Steedle, J. T. and Shavelson, R. J. 2010. Coefficient Alpha. Corsini Encyclopedia of Psychology. 1.

Author Information

  1. 1

    Council for Aid to Education, New York, NY

  2. 2

    Stanford University

Publication History

  1. Published Online: 30 JAN 2010


Because test scores are known to contain errors, test developers and administrators must concern themselves with test score consistency (or reliability). Such concerns are commonly investigated using coefficient alpha, an internal consistency reliability coefficient that is computed as follows:

  • mathml alt image

where k is the number of test items, inline image is the variance of scores on item i, and inline image is the variance of total test scores. Alpha is generally applicable for studying reliability on a single test at one point in time from multiple observations on individuals (e.g., scores on test items, task-performance ratings from multiple judges).


  • classical test theory;
  • generalizability theory;
  • reliability