Online Tools

Sample Size Calculators

DCR-4 Chapter 6 “Estimating Sample Size and Power” Appendixes A-F provide instructions and tables for calculating sample sizes.  However, the tables provided for two-group studies assume that the groups are of equal size.   If you have unequal group sizes (as occurs in most observational studies) or a study parameter that does not correspond to one of the table headings, then you may have to use one of these online calculators.

Online Calculators Corresponding to Tables in DCR-4 Chapter 6

Two-group analytic study comparing

(A) group means

(A-1) sample size given effect size

(A-2) effect size given sample size

(B) group proportions

(B-1) sample size given both proportions

(B-2) second proportion given sample sizes and first proportion

One-group analytic study comparing

(C) the correlation coefficient to zero (or another specified value)

One-group descriptive study estimating

(D) a mean

(E) a proportion

One-group analytic study comparing

(F) the mean change score to zero

Online Calculators Corresponding to Other Sample Size Problems