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Correlation · COR-CI

Sample Size for Estimation of Correlation

Plan the sample size needed to estimate a population correlation with a chosen absolute margin of error.

1. Information obtained from previous studies or literature

Use a relevant prior study, pilot estimate, or defensible planning value from −1 to 1.

2. Information decided by the researcher

Enter the desired absolute half-width on the correlation scale.

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

3. Results

Enter the correlation-estimation assumptions and select Calculate.

Formula, assumptions, limitations, and methodological note

Example clinical scenario

A researcher is planning a study of adults with hypertension to estimate the Pearson correlation between home systolic blood pressure and left ventricular mass index. The calculator determines how many participants are needed to estimate that correlation with the chosen confidence level and absolute margin of error.

Formula and methodological note

The calculator preserves the established normal-approximation precision formula based on the anticipated correlation, its variance factor, the selected confidence-level critical value, and the absolute margin of error.

It assumes paired continuous measurements from independent participants and a meaningful linear association. The planning correlation should come from relevant evidence or a defensible assumption.

The method does not account for clustering, design effects, missing-data mechanisms, non-linearity, measurement error, covariate adjustment, or a requested Fisher-z interval width. The result is rounded upward before dropout/non-response inflation.

Method references

  1. Bonett DG, Wright TA. Sample size requirements for estimating Pearson, Kendall and Spearman correlations. Psychometrika. 2000;65:23–28.
  2. Cohen J. Statistical Power Analysis for the Behavioral Sciences. 2nd ed. Hillsdale: Lawrence Erlbaum Associates; 1988.

Suggested citation

Yaacob, Najib Majdi. “Sample Size for Estimation of a Correlation (COR-CI).” Web calculator. NajibMY, 2026. Accessed July 29, 2026. https://najibmy.netlify.app/tools/sample-size/correlation/estimate-correlation/.