Calculating Sample Size for Ethics Applications using Instat


  • Open up InstatII
  • This gives you options: go to Sample size (statistical significance):

  • Enter the required information. This can be manipulated to get the sample size you’d like. Generally, estimated SD is about 10% and the minimum difference is 20%. The ethics just need to see you’ve put in a bit of effort.


  • Once you’ve done that, press Calculate. The a value is 0.05 and the b value you’d like is about 0.05 (power of 0.95).