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I have three groups with ~ 15 individuals per group.

  • Group 1 gets a treatment

  • Group 2 is a control in the same area

  • Group 3 is a further control in a different area

The response is binary, 1 or 0.

I want to determine the power of my study. I used this calculator but would like a second opinion. Using the terms from that site:

I have:

  • 2 independent study groups
  • A dichotomous endpoint
  • alpha = 0.05
  • power = 80%
  • 50% expected incidence in group 1
  • 10% expected incidence in group 2
  • an enrollment ratio of 2:1 because I lump my controls together (groups 2 and 3)

This gives a sample size of 14 for group 1 and 28 for group 2.

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