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**Objective: **We performed a double-blind, double-placebo–controlled, randomized trial involving women with idiopathic urgency urinary incontinence who had five or more episodes of urgency urinary incontinence per 3-day period, as recorded in a diary. For a 6-month period, participants were randomly assigned to daily oral anticholinergic medication (solifenacin, 5 mg initially, with possible escalation to 10 mg and, if necessary, subsequent switch to trospium XR, 60 mg) plus one intradetrusor injection of saline or one intradetrusor injection of 100 U of onabotulinumtoxinA plus daily oral placebo. The primary outcome was the reduction from baseline in mean episodes of urgency urinary incontinence per day over the 6-month period, as recorded in 3-day diaries submitted monthly. Secondary outcomes included complete resolution of urgency urinary incontinence, quality of life, use of catheters, and adverse events.

**Year:** 2012

**Source:** New England Journal of Medicine

**Link: **http://www.nejm.org/doi/full/10.1056/NEJMoa1208872

**Clinical Area: **Urology

Sample Size Section in Paper/Protocol: |

“A sample size of 242 subjects (121 per treatment group) provides at least 80% power to detect a relative difference of 53% between botulinum toxin A and standardized anticholinergic therapy, assuming a treatment difference of -0.80 and a common SD of 2.1 (effect size = 0.381), and a two-sided type I error rate of 5%. Sample size has been adjusted to allow for a 10% loss to follow-up over the 6-months of treatment as well as one interim analysis to stop early for benefit.” |

* Note:*

**Summary of Necessary Parameter Estimates for Sample Size Calculation:**

Parameter | Value |

Significance Level (2-Sided) | 0.05 |

Expected OnabotulinumtoxinA Mean | -2.3 |

Expected Antichollnergic Therapy Mean | -1.5 |

Standard Deviation (Both Groups) | 2.1 |

Power | 80% |

Number of Interim Analyses | 1 |

Alpha Spending Function (from Protocol) | O'Brien-Fleming |

Expected Dropout | 10% |

**Step 1: **

Select the **Group Sequential Test of Two Means **table from the Select Test Design & Goal window.

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 protocol.

Setting the **“Number of looks”** row to two specifies one interim analysis and one endpoint analysis.

**Step 3:**Click

This analysis calculates a sample size of 109 patients per group with a power of 80.15%. |

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

Output Statement: |

Sample sizes of 109 in group 1 and 109 in group 2 are required to achieve 80.16% power to detect a difference in means of -0.8 (the difference between group 1 mean, μ1, of -2.3 and group 2 mean, μ2, of -1.5) assuming that the standard deviation in group 1 is 2.1 and in group 2 is 2.1 using a two-sided z-test with 5% significance level. These results assume that the group sequential design has 1 interim sequential tests (2 total interim looks including final analysis) and the O'Brien-Fleming spending function is used to determine the efficacy test boundary. The drift parameter for this design equals 2.813. The drift parameter defines the increase in sample size needed over a fixed term design and equals square root of the maximum information level by the difference. |

**Step 5:**Calculate the sample size adjusted for expected 10% dropout, as outlined in protocol.

This gives a final sample size of 121 per group as per study design in protocol. |

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