Department of Statistics and Actuarial Science, University of Waterloo, Waterloo, Ontario, Canada. lwu@math.uwaterloo.ca|Department of Statistics and Actuarial Science, University of Waterloo, Waterloo, Ontario, Canada. lwu@math.uwaterloo.ca|Department of Statistics and Actuarial Science, University of Waterloo, Waterloo, Ontario, Canada. lwu@math.uwaterloo.ca|Department of Statistics and Actuarial Science, University of Waterloo, Waterloo, Ontario, Canada. lwu@math.uwaterloo.ca|Department of Statistics and Actuarial Science, University of Waterloo, Waterloo, Ontario, Canada. lwu@math.uwaterloo.ca