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Two replicate double blind, parallel-group, randomised controlled trials

**Objective: **Whether the combination of a once-daily inhaled corticosteroid with a once-daily longacting β2 agonist is more protective than a once-daily longacting β2 agonist alone against exacerbations of chronic obstructive pulmonary disease (COPD) is unknown. We hypothesised that fluticasone furoate and vilanterol would prevent more exacerbations than would vilanterol alone.

**Year:** 2013

**Source:** Lancet Respiratory Medicine

**Link: https://www.sciencedirect.com/science/article/abs/pii/S2213260013700407**

**Clinical Area: **Respiratory

Sample Size Section in Paper/Protocol: |

“On the basis of previous studies of fluticasone propionate–salmeterol combinations we assumed a yearly exacerbation rate with vilanterol of 1·4 and a dispersion parameter of 0·7. Thus, we calculated that a sample size of 390 assessable patients per group in each study would provide each study with 90% power to detect a 25% reduction in exacerbations in the fluticasone furoate and vilanterol groups versus the vilanterol only group at a two-sided 5% significance level” |

Summary of Necessary Parameter Estimates for Sample Size Calculation:

Parameter | Value |

Significance Level (2-Sided) | 0.05 |

Control Rate | 1.4 |

Rate Ratio | 0.75 |

Dispersion Parameter | 0.7 |

Exposure Time (Years) | 1 |

Power | 90% |

**Step 1:**Select the

This can be done **using the radio buttons** or alternatively, you can** use the search bar** at the end of the Select Test Design & Goal window.

**Step 2:**Enter the parameter values for sample size calculation taken from the study description.

**Step 3:**Select

The analysis calculates a sample size of 390 per group with 90.05% power, as per the study. |

**Step 4:**Once the calculation is completed, nQuery Advanced provides an output statement summarizing the results. It States:

Output Statement: |

The comparison of two event (incidence) rates using a Negative Binomial model with a group 1 sample size of 390 and a group 2 sample size of 390 achieves 90.05% power at the 0.05 significance level when the mean incidence rate in group 1 is 1.4 and the rate ratio is 0.75. This assumes the mean exposure time was 1 and the two groups have a common dispersion parameter of 0.7. This assumes the variance under the null hypothesis was calculated using the (Control Group Rate/True Rates/Maximum Likelihood) method |

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