Content Disclaimer
Copyright @2020.
All Rights Reserved.
StatsToDo : Sample Size for Two Counts : Explain, Calculations, and Tables

Links : Home Index (Subjects) Contact StatsToDo

Explanations Javascript Program Tables R Code
Please note that computation may take a long time if the sample size is large. On average, sample size less than 100 takes about 30 seconds. Time increases exponentially so that sample size of 200 may take 120 seconds, and further increase may take even hours.

Please note that some browsers have time limits, and when that limit is reached it asks the user whether to continue or not. Although long programs can be run, it does require the user to attend and repeatedly tell the browser to continue. The limits are as follows.

  • Internet Explorer - 5 million statements
  • Firefox - 10 secs
  • Safari - 5 secs
  • Chrome - no time limit
  • Opera - no time limit
Please note: that the calculations are for one tail studies.
Calculate Sample Size
Probability of Type I Error (α)
Power (1-β)
Count Rate Grp 1 (λ1)
Count Rate Grp 2 (λ2)
ratio (n1/n2)


Calculate Power
Probability of Type I Error (α)
Sample Size Group 1
Count Group 1
Sample Size Group 2
Count Group 2