If none of the boundaries are crossed it may also be useful to examine the conditional power or stopping probabilities of future stages. If none of the boundaries are crossed the study continues to the next stage. Typically, if one of the boundaries is crossed, the study is stopped (non-binding futility boundaries may be an exception). The stage one z-statistic is compared to each of the stage one boundaries. The analysis at this point is called the first stage.Ī z-statistic (or in some cases t-) is calculated from the raw data. The study begins, and response data is collected for subjects, moving toward the first-stage target number of subjects, until a decision to perform an analysis on the existing data is made. The design phase gives the target number of subjects for the first stage. We refer the user to the PASS software and corresponding documentation for more details on sample size estimation. This calculation requires the input of a number of parameters, including desired alpha, power, boundary types, maximum number of stages, spending functions, and assumed differences, among others. Corresponding to each NCSS procedure for group-sequential analysis, there exists a companion procedure in PASS Sample Size software for making this calculation. In the design phase, an initial calculation of the sample size needed (if the final stage is reached) is made. Technical Detailsįor in depth details of a group-sequential analysis, we refer the reader to the 'Documentation PDF' of each procedure, along with the referenced materials in that documentation. A group-sequential plot may be used to show the current progress of a group-sequential analysis.īoundaries may be determined for either efficacy (significant difference), or futility (lack of evidence of difference), or both (as shown in the plot). Boundaries for each stage are determined by the amount of data collected to that point (the information) and the amount of alpha or beta spent, as determined by the spending function(s). To accommodate this, and to maintain proper error control, the specified alpha and/or beta is apportioned according to appropriate alpha- or beta-spending functions. Group-sequential analysis permits one to evaluate significant statistical difference at any stage in data collection. When data is gathered over time, it can be useful to make statistical comparisons when only portions of the data have been collected. Group-Sequential Analysis for Two Hazard Rates.Group-Sequential Analysis for Two Proportions.Group-Sequential Analysis for Two Means with Known Variances.For details about the initial sample size estimation in PASS, as well as other general group-sequential testing details, click here. To see how these tools can benefit you, we recommend you download and install the free trial of NCSS. Use the links below to jump to the group-sequential analysis topic you would like to examine. The group-sequential analysis procedures in NCSS are easy-to-use and validated for accuracy. Tools are also available for non-inferiority and superiority by a margin tests. NCSS includes tools for performing group-sequential analysis of one or two means, two proportions, and two hazard rates.
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