**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**