Department of Biostatistics Seminar/Workshop Series

# A Mighty Wind, Etc; A talk in two parts

### Intended Audience: Persons interested in applied statistics, statistical theory, epidemiology, health services research, clinical trials methodology, statistical computing, statistical graphics, R users or potential users

Part 1: You’re standing on a street corner in Nashville, and the next thing you know you’ve been transported to Paris. (Talk about a mighty wind!) If we regard Earth as a unit sphere, a move to Paris from Nashville may be viewed as an “orthogonal transformation”. Such a transformation is represented by a 3 x 3 orthogonal matrix, and may be regarded as a “rotation” from one place to another. If the initial rotation from Nashville is random and uniformly distributed (I’ll explain what I mean by this), you could have ended up anywhere. – in the sense that your location is uniformly distributed on the surface of the unit sphere. (That you happened to land in Paris is pure luck!) Now, suppose that the same transformation is used to rotate you again to a new place on the unit sphere. What can you say about where you are now? (Have you moved back closer to Nashville, for example, or could you still be anywhere?) And what if this keeps happening to you, again and again? (A connection will be drawn, albeit loosely, with a common distribution on the sphere used to model directional data.)

Part 2: Here’s a simply worded problem, but one for which a really satisfactory solution seems elusive. Given a random sample from a k-variate normal distribution with unknown mean vector and unknown covariance matrix, produce a confidence interval for the maximum component of the mean vector. I’ll motivate this problem by describing what a regulatory guidance says should be done when analyzing data collected in a “thorough QT study”, and describe an approach which works well in some circumstances. (Q and T are two points on an electrocardiogram (ECG), and the duration of the interval between them, the “QT interval” represents the working phase of the heart -- when the heart is contracting. In the pharmaceutical industry, studies that indicate significant QT prolongation are often sufficient for a company to discontinue development of a compound.)
Topic revision: r2 - 26 Apr 2013, JohnBock

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