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\centerline{\bf STANFORD UNIVERSITY}
\centerline{\bf DEPARTMENT OF STATISTICS}
\centerline{\big DEPARTMENTAL SEMINAR}
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\centerline{4:15 p.m., Tuesday, March 6, 2001}
\centerline{Sequoia Hall Rm. 200}
\centerline{(Cookies at 3:45 in 1st Floor Lounge)}

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\centerline{\sl Bradley Efron}
\centerline{\sl Department of Statistics}
\centerline{\sl Stanford University}
\centerline{\sl Stanford,  CA 94305}
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\centerline{\bf The Two-Way Proportional Hazards Model}

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Survival analysis problems often involve dual time scales, calendar
date and lifetime, the latter being the elapsed time since an initiating
event such as HIV infection. The motivating example for this talk involved
620 organ transplant patients, 110 of whom suffered a serious bacterial
infection at some time following the transplant. The main question of 
interest
was whether the incidence rate of bacterial infection was declining over
the 16 years of study. Different answers to this question are possible,
depending on whether the proportional hazards analysis is carried out on
the calendar date or lifetime scale. The "two-way" model tries to look at
the problem symmetrically, combining the information from both time scales
in an efficient manner.

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