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Reliability & Agreement · ALPHA-CI

Sample Size for Estimation of Cronbach Alpha

Plan a sample size to estimate Cronbach alpha reliability with a chosen confidence level and margin of error.

1. Information obtained from previous studies or literature

Use a prior study, pilot estimate, or defensible planning value.

2. Information decided by the researcher

The method uses full interval width; this calculator sets width to twice the margin of error.

Defaults to 10%. Enter 0 if no adjustment is required.

3. Results

Enter the planning assumptions and select Calculate.

Formula, assumptions, limitations, and methodological note

Example clinical scenario

A researcher develops a diabetes self-management questionnaire and wants to estimate Cronbach alpha with a confidence interval of prespecified precision.

Formula and methodological note

This calculator uses the preserved published approximation documented in the calculator specification. It assumes the selected reliability or agreement model, independent subjects, the stated number of items or ratings, and defensible planning values.

Sample size is rounded upward before the dropout/non-response adjustment, which is also rounded upward. The method does not replace design-specific review for clustered samples, multiple raters beyond the stated model, missing ratings, weighted kappa, ordinal outcomes, or alternative ICC definitions.

Method references

  1. Bonett DG. Sample size requirements for testing and estimating coefficient alpha. J Educ Behav Stat. 2002;27(4):335–340.
  2. Bonett DG, Wright TA. Sample size requirements for estimating Pearson, Kendall and Spearman correlations. Psychometrika. 2000;65(1):23–28.

Suggested citation

Yaacob, Najib Majdi. “Sample Size for Estimation of Cronbach Alpha (ALPHA-CI).” Web calculator. NajibMY, 2026. Accessed July 29, 2026. http://127.0.0.1:4321/tools/sample-size/reliability-agreement/estimate-cronbach-alpha/.