Select the method or formula of your choice.

One-sided power ( *H* _{1}: *λ*_{1} > *λ*_{2})

One-sided power ( *H* _{1}: *λ*_{1} < * λ*_{2})

Two-sided power ( *H* _{1}: *λ*_{1} ≠ *λ*_{2})

Term | Description |
---|---|

Φ | the cumulative distribution function (CDF) of the standard normal distribution |

z _{α} | Φ ^{-1} (1- α) where Φ ^{-1} is the inverse CDF of the standard normal distribution |

λ _{1} | the comparison rate |

λ _{2} | the baseline rate |

σ _{0} | standard deviation under null hypothesis: |

σ _{A} | standard deviation under alternative hypothesis: |

t _{1} | length for group 1 |

t _{2} | length for group 2 |

If you provide values for power and sample size, Minitab calculates the value of the comparison rate. If you provide values for power and comparison rate, Minitab calculates the value of the sample size.

For these two cases, Minitab uses an iterative algorithm to find the optimal value. At each iteration, Minitab evaluates the power for a trial sample size or trial comparison rate, and stops when the power function equals a target power value.

When Minitab calculates sample size, it may find that no integer value of sample size yields your target power. In such cases, Minitab displays the target value for power alongside the actual power, which is a value corresponding to an integer sample size, and which is nearest to, yet greater than, the target value.