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Reliability & Agreement · ICC-CI

Sample Size for Estimation of Intraclass Correlation Coefficient

Plan a sample size to estimate ICC reliability with a chosen confidence level and total interval width.

1. Information obtained from previous studies or literature

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

2. Information decided by the researcher

Enter the full interval width, not the half-width.

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

Two physiotherapists repeatedly measure knee range of motion in the same patients, and the researcher wants to estimate the intraclass correlation coefficient with specified 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 estimating intraclass correlations with desired precision. Stat Med. 2002;21(9):1331–1335.
  2. Walter SD, Eliasziw M, Donner A. Sample size and optimal designs for reliability studies. Stat Med. 1998;17(1):101–110.

Suggested citation

Yaacob, Najib Majdi. “Sample Size for Estimation of Intraclass Correlation Coefficient (ICC-CI).” Web calculator. NajibMY, 2026. Accessed July 29, 2026. http://127.0.0.1:4321/tools/sample-size/reliability-agreement/estimate-intraclass-correlation-coefficient/.