search for: albyn

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2011 Apr 18
Power Analysis
I am trying to do a power analysis to get the number of replicas per treatment. If I try to get the power it works just fine: setn=c(2,3) sdx=c(1.19,4.35) power.t.test(n = setn, delta = 13.5, sd = sdx, sig.level = 0.05,power = NULL) If I go the other way to obtain the "n" I have problems. sdx=c(1.19,4.35) pow=c(.8,.8) power.t.test(n = NULL, delta = 13.5, sd = sdx, sig.level = 0.05,
2010 May 10
Random walk
Hi everybody, I am trying to generate two random walks with an specific correlation, for example, two random walks of 200 time steps with a correlation 0.7. I built the random walks with: x<-cumsum(rnorm(200, mean=0,sd=1)) y<-cumsum(rnorm(200, mean=0,sd=1)) but I don't know how to fix the correlation between them. With white noise is easy to fix the correlation using the function
2011 May 27
"useR! 2011" T-shirt competition
Dear R users: We are looking for a new design for the front of the "useR! 2011" conference T-shirt, and we invite submissions by June 13. It is planned that participants in the R User Conference, useR! 2011 (August 16-18, will each receive a T-shirt, thanks to the sponsorship of Mango Solutions
2010 Dec 02
Integral of PDF
The integral of any probability density from -Inf to Inf should equal 1, correct? I don't understand last result below. > integrate(function(x) dnorm(x, 0,1), -Inf, Inf) 1 with absolute error < 9.4e-05 > integrate(function(x) dnorm(x, 100,10), -Inf, Inf) 1 with absolute error < 0.00012 > integrate(function(x) dnorm(x, 500,50), -Inf, Inf) 8.410947e-11 with absolute error <
2013 Aug 30
When I try to apply mean to a list, I get the answer : argument is not numeric or logical: returning NA Could you help me? (I am a very beginner) -- View this message in context: Sent from the R help mailing list archive at
2013 May 23
sample(c(0, 1)...) vs. rbinom
Greetings.? My wife is teaching an introductory stat class at UC Davis.? The class emphasizes the use of simulations, rather than mathematics, to get insight into statistics, and R is the mandated tool.?? A student in the class recently inquired about different approaches to sampling from a binomial distribution.? I've appended some code that exhibits the idea, the gist of which is that using
2002 Oct 09
Summary Orthogonal Polynomials
As usual, the R newsgroup set me straight (thanks to Douglas Bates, Robert Balshaw and Albyn Jones). There is really no difference between using orthogonal polynomials of the form: Linear -3 -1 1 3 Quadratic 1 -1 -1 1 Cubic -1 3 -3 1 Versus > poly(c(1:4),3) 1 2 3 [1,] -0.6708204 0.5 -0.2236068 [2,] -0.2236068 -0.5 0.6708204 [3,] 0....
2010 Sep 13
The future of R - Ross Ihaka stirs discussions around the web
Hello all, There is currently a (very !) lively discussions happening around the web, surrounding the following topics: 1) Is R efficient? (scripting wise, and performance wise) 2) Should R be written from scratch? 3) What should be the license of R (if it was made a new)? Very serious people have taken part in the debates so far. I hope to let you know of the places I came by, so you might be
2006 Jun 19
Foometrics in R
One of the outcomes of useR! 2006 is that JSS is planning to publish a series of special volumes. They will be guest edited (I have guest editors already, although somewhat tentative in some cases). Each volume will have 5-10 issues (articles) of the usual JSS format. Psychometrics in R Political Methodology in R Econometrics in R Social Science Methodology in R Spectroscopy/Chemometrics in R
2008 Dec 19
comparing distributions
I have data sets from three different sites. None of the data sets are normally distributed and can not be log-transformed to a normal distribution. I would like to compare the data sets to see if any of the sites are similar to each other, and would like something more powerful than a non-parametric wilcoxen test. Does anyone have any suggestions on more powerful ways of comparing non-normal data
2011 Aug 19
Calculating p-value for 1-tailed test in a linear model
Hello, I'm having trouble figuring out how to calculate a p-value for a 1-tailed test of beta_1 in a linear model fit using command lm. My model has only 1 continuous, predictor variable. I want to test the null hypothesis beta_1 is >= 0. I can calculate the p-value for a 2-tailed test using the code "2*pt(-abs(t-value), df=degrees.freedom)", where t-value and degrees.freedom
2009 Feb 28
Extract statistics from lm()
Hi, perhaps this question was answered previously however I could not find them. My problem is how how to extract a particular statistic from the result given by lm(). For e.g. ctl <- c(4.17,5.58,5.18,6.11,4.50,4.61,5.17,4.53,5.33,5.14) trt <- c(4.81,4.17,4.41,3.59,5.87,3.83,6.03,4.89,4.32,4.69) group <- gl(2,10,20, labels=c("Ctl","Trt")) weight <- c(ctl, trt) >
2009 Jul 30
truncating values into separate categories
Hi all, Simple question which i thought i had the answer but it isnt so simple for some reason. I am sure someone can easily help. I would like to categorize the values in NP into 1 of the five values in "Per", with the last category("4") representing values >=4(hence 4:max(NP)). The problem is that R is reading max(NP) as multiple values instead of range so the
2009 Mar 10
Cholesky Decomposition in R
Hi everyone: I try to use r to do the Cholesky Decomposition,which is A=LDL',so far I only found how to decomposite A in to LL' by using chol(A),the function Cholesky(A) doesnt work,any one know other command to decomposte A in to LDL' My r code is: library(Matrix) A=matrix(c(1,1,1,1,5,5,1,5,14),nrow=3) > chol(A) [,1] [,2] [,3] [1,] 1 1 1 [2,] 0 2 2
2001 Sep 03
mixture distributions
Dear List, I am looking for a possibility to fit a mixture model under R using maximum likelihood estimation. Venables and Ripley describe a solution working under S+ (in MASS, 3. ed., p. 263) which requires the D system function and deriv3. This solution does not seem to be portable to R or at least I do not realise how. Is there anyone who a) knows how one could make the MASS-method run under