Dear List I am using R with mcgv package to model spatial variation in density estimates of dorcas gazelle in Sinai. I have 59 points of data and 4 explanatory variables(distance from mountain edge, camel presence, Latitude & Longitude). I want to test the model fir via bootstraping. I have used the jacknife bootstraping but it have the limitation of allowing only 58 trials. I tried to use the bootstrap function in R but I couldn;t understand the help file description. Please forgive my novice with such advance statistics since I am a biologist. I would appreciate any help on advicing on how to use the bootstrap function in R. Thanks in advance Husam El Alqamy ---------------------------------------- Biologist Ranger St. Katherine Protectorate South Sinai, EGYPT ---------------------------------------- tel 002-069-470032 Fax 002-069-470033 ---------------------------------------- -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
Date: Thu, 31 Jan 2002 15:34:55 +0200 From: "Husam Alqamy" <alqamy at lycos.com> Mime-Version: 1.0 X-Sent-Mail: off Reply-To: alqamy at lycos.com X-Mailer: MailCity Service X-Priority: 3 X-Sender-Ip: 213.131.66.41 Organization: Lycos Mail (http://mail.lycos.com:80) Content-Type: text/plain; charset=us-ascii Content-Language: en Content-Transfer-Encoding: 7bit Sender: owner-r-help at stat.math.ethz.ch Precedence: SfS-bulk Dear List I am using R with mcgv package to model spatial variation in density estimates of dorcas gazelle in Sinai. I have 59 points of data and 4 explanatory variables(distance from mountain edge, camel presence, Latitude & Longitude). I want to test the model fir via bootstraping. I have used the jacknife bootstraping but it have the limitation of allowing only 58 trials. I tried to use the bootstrap function in R but I couldn;t understand the help file description. Please forgive my novice with such advance statistics since I am a biologist. I would appreciate any help on advicing on how to use the bootstrap function in R. Thanks in advance Husam El Alqamy ---------------------------------------- Biologist Ranger St. Katherine Protectorate South Sinai, EGYPT ---------------------------------------- tel 002-069-470032 Fax 002-069-470033 ---------------------------------------- -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._ Just a off-topic comment. With only 59 points but 4 variables, you are stretched very very thin using a nonparametric method. Bootstrap isn't going to bring in more information. If I were you, I would try to find some parametric model to fit to the data. Chong Gu -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
> I am using R with mcgv package to model spatial variation in density estimates of dorcas gazelle in Sinai. I have 59 points of data and 4 explanatory variables(distance from mountain edge, camel presence, Latitude & Longitude). I want to test the model fir via bootstraping. I have used the jacknife bootstraping but it have the limitation of allowing only 58 trials. I tried to use the bootstrap function in R but I couldn;t understand the help file description. Please forgive my novice with such advance statistics since I am a biologist. > I would appreciate any help on advicing on how to use the bootstrap function in R. > Thanks in advance > Husam El Alqamy- 59 datapoints is really pushing it for estimating 4 functions! You might want to run the first bit of the code pasted below a few times to see if this is really good enough for you [it's actually not as bad as I assumed it was going to be]. - If you want a *really* simple bootstrap then the second part of the code below gives an example: but for this sample size, the effect of neglecting the bias in the fitted values and the variability in the variance estimate will not be negligible! - Finally, note that bootstrapping non-parametrically (i.e. case resampling) would be a bit of a disaster in this case, since the smoothing parameters are being selected by cross validation. Simon. # fit model to simulated data.... n<-59 sig2<-4 x0 <- runif(n, 0, 1) x1 <- runif(n, 0, 1) x2 <- runif(n, 0, 1) x3 <- runif(n, 0, 1) pi <- asin(1) * 2 f <- 2 * sin(pi * x0) f <- f + exp(2 * x1) - 3.75887 f <- f + 0.2 * x2^11 * (10 * (1 - x2))^6 + 10 * (10 * x2)^3 * (1 - x2)^10-1.396 e <- rnorm(n, 0, sqrt(abs(sig2))) y <- f + e da<-data.frame(y=y,x0=x0,x1=x1,x2=x2,x3=x3) b<-gam(y~s(x0)+s(x1)+s(x2)+s(x3),data=da) plot(b,pages=1) # now a crude parametric bootstrap.... model.mean<-fitted(b) model.se<-b$sig2^0.5 for (i in 1:20) { da$y<-model.mean+rnorm(n,sd=model.se) b.bs<-gam(y~s(x0)+s(x1)+s(x2)+s(x3),data=da) plot(b.bs,pages=1) } ______________________________________________________________________> Simon Wood snw at st-and.ac.uk http://www.ruwpa.st-and.ac.uk/simon.html > The Mathematical Institute, North Haugh, St. Andrews, Fife KY16 9SS UK > Direct telephone: (0)1334 463799 Indirect fax: (0)1334 463748-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._