Hi all, Running the following code:> n <- 25 > y0 <- rpois(n, 0.04) > y1 <- rpois(n, 0.34) > > resp <- c(y0, y1) > group <- c(rep(0,n), rep(1,n)) > > wilcox.test(y0, y1)Wilcoxon rank sum test with continuity correction data: y0 and y1 W = 250, p-value = 0.02074 alternative hypothesis: true mu is not equal to 0 Warning message: Cannot compute exact p-value with ties in: wilcox.test.default(y0, y1)> > glm.M1 <- glm(resp ~ group, family=poisson()) > summary(glm.M1)Call: glm(formula = resp ~ group, family = poisson()) Deviance Residuals: Min 1Q Median 3Q Max -0.692820 -0.692820 -0.004968 -0.004968 2.227342 Coefficients: Estimate Std. Error z value Pr(>|z|) (Intercept) -11.303 34.531 -0.327 0.743 group 9.875 34.533 0.286 0.775 (Dispersion parameter for poisson family taken to be 1) Null deviance: 28.216 on 49 degrees of freedom Residual deviance: 19.899 on 48 degrees of freedom AIC: 34.512 Number of Fisher Scoring iterations: 9>I would interpretate this that the Wilcoxon detect a group difference, while glm not. I expected the beta for the group greater than zero. Can somebody explain me such a difference in two methods of rejecting a hypothesis? Where am I wrong? Kind regards, Dominik -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- 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 _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
Hi all, running the following code:> n <- 25 > y0 <- rpois(n, 0.04) > y1 <- rpois(n, 0.34) > > resp <- c(y0, y1) > group <- c(rep(0,n), rep(1,n)) > > wilcox.test(y0, y1)Wilcoxon rank sum test with continuity correction data: y0 and y1 W = 250, p-value = 0.02074 alternative hypothesis: true mu is not equal to 0 Warning message: Cannot compute exact p-value with ties in: wilcox.test.default(y0, y1)> > glm.M1 <- glm(resp ~ group, family=poisson()) > summary(glm.M1)Call: glm(formula = resp ~ group, family = poisson()) Deviance Residuals: Min 1Q Median 3Q Max -0.692820 -0.692820 -0.004968 -0.004968 2.227342 Coefficients: Estimate Std. Error z value Pr(>|z|) (Intercept) -11.303 34.531 -0.327 0.743 group 9.875 34.533 0.286 0.775 (Dispersion parameter for poisson family taken to be 1) Null deviance: 28.216 on 49 degrees of freedom Residual deviance: 19.899 on 48 degrees of freedom AIC: 34.512 Number of Fisher Scoring iterations: 9 I would interpretate this that the Wilcoxon detect a group difference, while glm not. I expected the beta for the group greater than zero. Can somebody explain me such an difference of two methods of rejecting a hypothesis? Where am I wrong? Regards, Dominik -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- 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 _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
On Mon, 25 Feb 2002, Dominik Grathwohl wrote:> Hi all, > running the following code: > > n <- 25 > > y0 <- rpois(n, 0.04) > > y1 <- rpois(n, 0.34) > > > > resp <- c(y0, y1) > > group <- c(rep(0,n), rep(1,n)) > > > > wilcox.test(y0, y1) > > Wilcoxon rank sum test with continuity > correction > > data: y0 and y1 > W = 250, p-value = 0.02074 > alternative hypothesis: true mu is not equal to 0 > > Warning message: > Cannot compute exact p-value with ties in: > wilcox.test.default(y0, y1) > > > > glm.M1 <- glm(resp ~ group, family=poisson()) > > summary(glm.M1) > > Call: > glm(formula = resp ~ group, family = poisson()) > > Deviance Residuals: > Min 1Q Median 3Q > Max > -0.692820 -0.692820 -0.004968 -0.004968 > 2.227342 > > Coefficients: > Estimate Std. Error z value Pr(>|z|) > (Intercept) -11.303 34.531 -0.327 0.743 > group 9.875 34.533 0.286 0.775 > > (Dispersion parameter for poisson family taken to > be 1) > > Null deviance: 28.216 on 49 degrees of > freedom > Residual deviance: 19.899 on 48 degrees of > freedom > AIC: 34.512 > > Number of Fisher Scoring iterations: 9 > > I would interpretate this that the Wilcoxon detect > a group difference, while glm not. I expected the > beta for the group greater than zero. > Can somebody explain me such an difference of two > methods of rejecting a hypothesis? Where am I > wrong?If you take a look at your simulated data, you will probably guess the answer.> > Regards, > > Dominik > > -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- > 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 > _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._ >-- G?ran Brostr?m tel: +46 90 786 5223 professor fax: +46 90 786 6614 Department of Statistics http://www.stat.umu.se/egna/gb/ Ume? University SE-90187 Ume?, Sweden e-mail: gb at stat.umu.se -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- 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 _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
Dear Thomas, dear Prof. Ripley, The likelihood ratio test (28.216 - 19.899 on 1df) did the job well:>1-pchisq(8.3171,1)[1] 0.003927357 And thanks for the warning in analysing sparse events. Dominik -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- 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 _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._