The views expressed here are those of the individual authors and not necessarily those of the JSM sponsors, their officers, or their staff.
Abstract Details
Activity Number:
|
478
|
Type:
|
Contributed
|
Date/Time:
|
Wednesday, August 3, 2011 : 8:30 AM to 10:20 AM
|
Sponsor:
|
Section on Statistics and the Environment
|
Abstract - #302562 |
Title:
|
Modeling Aspen Tree Mortality Using Modified GEE Approach for Irregular Time Intervals
|
Author(s):
|
Suborna Shekhor Ahmed*+ and Valerie LeMay and Changhui Peng and Zhihai Ma
|
Companies:
|
University of British Columbia and University of British Columbia and University of Quebec at Montreal and University of Quebec at Montreal
|
Address:
|
2424 Main Mall, Forest Sciences Centre, Vancouver, BC, V6T1Z4, Canada
|
Keywords:
|
irregular time intervals ;
modified GEE ;
maximum likelihood estimator ;
modified logistic regression ;
survival analysis ;
autocorrelation
|
Abstract:
|
A probability of survival model was used to predict regular mortality of the aspen (Populus tremuloides Michx) tree species in Alberta, Canada. For tree survival, commonly permanent sample plot (PSP) data with repeated measures of individual trees at irregular time intervals are used. As a result, the logistic model was modified for survival under irregular time intervals (Modified Logistic Model). Also, autocorrelation within trees under irregular time intervals was addressed by developing a modified Generalized Estimating Equations (GEE) approach. In the Modified GEE approach, the error correlation structure was adjusted using the tree-specific time intervals. The Maximum Likelihood estimator for the Modified Logistic Model assuming no autocorrelation was used to obtain the initial estimate of the vector of model parameters. Then, the Modified Logistic Model was fit using the modified GEE approach to obtain final estimates. Monte Carlo simulations indicate that the resulting estimators are approximately unbiased and are reasonably precise.
|
The address information is for the authors that have a + after their name.
Authors who are presenting talks have a * after their name.
Back to the full JSM 2011 program
|
2011 JSM Online Program Home
For information, contact jsm@amstat.org or phone (888) 231-3473.
If you have questions about the Continuing Education program, please contact the Education Department.