Sample Size Calculator for Comparing Two Independent Means

  • Provides live interpretations.
  • Evaluates the influence of changing input values.
  • Adjusts sample sizes for continuity and clustering.

Input Values

Select one of the two options to specify input values. Hover over for help.

Mean of the Reference Group:
Mean of the Test Group:
Standard Deviation:
Difference between Two Means:
Expected Standard Deviation:

Click the Options button to change the default options for Power, Significance, Alternate Hypothesis and Group Sizes. Use the Adjust button to adjust sample sizes for t-distribution (option applied by default), and clustering.
 

Influence of Changing Input values on Sample Size Estimates

Customize Visualisation

Customize the plot by changing input values from here.

From Min
To Max
By
1st Series
2nd Series
3rd Series

Note: You may change the default options for Power, Significance, Alternate Hypothesis and Group Sizes by clicking the 'Options' button. You may also adjust the calculated sample size for t-distribution or clustering using the 'Adjust' button.

Visualisation

This is a plot of sample sizes for a range of pooled Standard Deviations and for three values of Difference of means between groups. Customize the plot by changing input values from the 'Customize Visualisation' panel.

Download Figure

Table of Sample Sizes at a range of Expected Means.

Customize Table

Customize the table by changing input values from here.

From Min
To Max
By
From Min
To Max
By

Note: You may change the default options for Power, Significance, Alternate Hypothesis and Group Sizes by clicking the 'Options' button. You may also adjust the calculated sample size for t-distribution or clustering using the 'Adjust' button.

Sample Size Table

This table shows sample sizes for a range of expected means in the two groups. Customize the table by changing input values from the 'Customize Table' pane.

Download Table