Dear Tim, Thank you so much for addressing all my questions. This really makes sense.
I talked with my advisor yesterday about how to do bootstrapping for my scenario: random clinic + random subject within clinic. She suggested that only clinic are independent units, so I can only resample clinic. But I think that since subjects are also independent within clinic, shall I resample subjects within clinic, which means I have two-stage resampling? Which one do you think makes sense? Thank you very much and I look forward to hearing from you. Qian On 31 Mar 2005, Tim Hesterberg wrote: > Dear Qian, > > Yes, when bootstrap sampling by subject, when a subject is included > in a bootstrap dataset multiple times, you must give that subject > different IDs, or some statistics would be incorrect. > > Here's what S+Resample does (from help(bootstrap.args)): > If subject is the name of a variable in the data frame (for > example data=Orthodont, subject=Subject), then bootstrap makes > resampled subjects unique; that is, duplicated subjects in a > given resample are assigned distinct subject values in the > resampled data frame before the statistic is evaluated; this is > useful for longitudinal and other modeling where the statistic > expects subjects to have unique values. > > Tim Hesterberg > > > >Dear Tim, > > > >Thank you so much for your help. My random mixed model is as follows: > > > >b.lme <- lme(sbp ~ age + gender, data=bdat, random=~1/clinic/id, > > na.action=na.omit) > > > >When doing bootstrap with stratum clinic, a patient's data may appear > >multiple times in the boostrap dataset and all of them share the same id. > >I am wondering if the data from the same patient will cause problems in > >lme fitting or not. Do you happen to know this or not? > > > >Sincerely yours, > >Qian > > ======================================================== > | Tim Hesterberg Research Scientist | > | [EMAIL PROTECTED] Insightful Corp. | > | (206)802-2319 1700 Westlake Ave. N, Suite 500 | > | (206)283-8691 (fax) Seattle, WA 98109-3044, U.S.A. | > | www.insightful.com/Hesterberg | > ======================================================== > Download the S+Resample library from www.insightful.com/downloads/libraries > > *************************************** Qian An Division of Biostatistics University of Minnesota (phone) 612-626-2263 (fax) 612-626-8892 Email: [EMAIL PROTECTED] ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
