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Version 1.2.2, Last Modified Date: 12/11/2012


TTEDesigner: Designing one-arm time-to-event safety monitoring trials

This software is for designing single-arm safety monitoring trials with time-to-event outcomes and a single arm. Time to event is modeled as exponential, with mean distributed as inverse gamma. The trial stops if and when the posterior probability is sufficiently large that the experimental treatment is worse than a historical standard. The event being monitored is often something bad, like disease progression, in which case you want to maximize time to event. But the event can also be something good, like engraftment, in which case you want to minimize the time to event. This simple model is surprisingly robust, as demonstrated in [1].

Most of the parameters in the design have clear interpretations and rules of thumb for filling them in. You can get suggestions for filling in parameters by clicking on links in the software. But there's one cutoff parameter that isn't obvious how to set. Typically people run a dozen simulations, tweaking this parameter until they get the operating characteristics they want. TTEDesigner seeks to eliminate that process.  Instead of entering cutoff parameter values, you enter the operating characteristics you want and let the software solve for the parameter that best meets those characteristics.

As with everything else in statistics, it's usually not possible to satisfy everything at once. Everyone wants tiny trials with small type I and type II error. This software will let you satisfy two out of three criteria:

  1. Sample size
  2. Stopping percentage under bad scenario
  3. Stopping percentage under good scenario

So for a given sample size, it will come up with a cutoff parameter that will exactly satisfy (2) and another parameter that will exactly satisfy (3). It also gives three compromise designs for values in between these extremes for a total of five designs. Select one of these five designs, and it will give you a table of stopping boundaries like that in TTEConduct.


TTEDesigner screen shot

See the TTEDesigner user's manual for more details.

Clift Norris developed the user interface for TTEDesigner using C#. Leiko H. Wooten and John Cook developed the statistical calculations using Visual C++.

What's new in v1.2.2?

  • IMPORTANT: DO NOT USE v1.2.1. A bug introduced in v1.2.1 led to bad simulation results. This is fixed in v1.2.2.
  • Improved text.


  1. Peter F. Thall, Leiko H. Wooten, and Nizar M. Tannir. Monitoring Event Times in Early Phase Clinical Trials: Some Practical Issues, Clinical Trials 2, 467-478 (2005).