search for: dxi

Displaying 20 results from an estimated 89 matches for "dxi".

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2011 Aug 19
1
help Dxy and C-index calculation
Dear professor, I am currently using Design package and the cph formula for assessing multivariable analysis. I am tryng to get the C-index for my survival model based on Dxy coefficient. I am confused since there is a negative value. Do I need to used the absolute Dxy ? index.orig training test optimism index.corrected n Dxy -0.341357727 -0.344002740
2011 Jun 13
1
Somers Dyx
Hello R Community, I'm continuing to work through logistic regression (thanks for all the help on score test) and have come up against a new opposition. I'm trying to compute Somers Dyx as some suggest this is the preferred method to Somers Dxy (Demaris, 1992). I have searchered the [R] archieves to no avail for a function or code to compute Dyx (not Dxy). The overview of Hmisc has
2006 Jul 27
1
replace values in a distance matrix
Hi to everybody! I´m just a beginner in R, and I´m trying to replace values in a distance matrix with a concret condition: replace all values (elements) lower than 4.5 with value=18. I´ve tried this, but it doesn´t work... Dxy would be my 117 x 117 euclidean distance matrix M18 and M4.5 would be 117 x 117 matrices: M18<-matrix(rep(18,13689),nrow=117)
2009 Jul 15
1
negative Somers D from Design package
Dear R help My problem is very similar to the analysis detailed here. If we use the mayo dataset provided with the survivalROC package the estimate for Somer's Dxy is very negative -0.56. The Nagelkerke R2 is positive though 0.32. I know there is a difference between explained variation and predictive ability but I am surprised there is usch a difference given that even a non predictive model
2005 Nov 03
1
How to calculate errors in histogram values
Hi there, I'm new to R but I thought this is the most likely place I could get advice or hints w.r.t the following problem: I have a series of measurements xi with associated uncertainties dxi. I would like to construct the probability density histogram of this data where each density estimate has an associated error that is derived from the dxi. In other words, for large dxi the histogram should also display large uncertainties and vice versa. I need this for a curve fitting algorit...
2019 Oct 29
5
head.matrix can return 1000s of columns -- limit to n or add new argument?
...all dimensions") if(!is.null(dim(x))) dimsx <- dim(x) else dimsx <- length(x) ## this returns a list of vectors of indices in each ## dimension, regardless of length of the the n ## argument sel <- lapply(seq_along(dimsx), function(i) { dxi <- dimsx[i] ## select all indices (full dim) if not specified ni <- if(length(n) >= i) n[i] else dxi ## handle negative ns ni <- if (ni < 0L) max(dxi + ni, 0L) else min(ni, dxi) seq.int(to = dxi, length.out = ni) }) args <- c(list(x)...
2011 Feb 21
2
Interpreting the example given by Prof Frank Harrell in {Design} validate.cph
Dear R-help, I am having a problem with the interpretation of result from validate.cph in the Design package. My purpose is to fit a cox model and validate the Somer's Dxy. I used the hypothetical data given in the help manual with modification to the cox model fit. My research problem is very similar to this example. This is the model without stratification: > library(Design) > f1
2007 Aug 27
2
validate (package Design): error message "subscript out of bounds"
Dear R users I use Windows XP, R2.5.1 (I have read the posting guide, I have contacted the package maintainer first, it is not homework). In a research project on renal cell carcinoma we want to compute Harrell's c index, with optimism correction, for a multivariate Cox regression and also for some univariate Cox models. For some of these univariate models I have encountered an error
2011 Mar 01
1
which does the "S.D." returned by {Hmisc} rcorr.cens measure?
Dear R-help, This is an example in the {Hmisc} manual under rcorr.cens function: > set.seed(1) > x <- round(rnorm(200)) > y <- rnorm(200) > round(rcorr.cens(x, y, outx=F),4) C Index Dxy S.D. n missing uncensored Relevant Pairs Concordant Uncertain 0.4831 -0.0338 0.0462 200.0000
2009 Sep 08
1
rcorrp.cens and U statistics
I have two alternative Cox models with C-statistics 0.72 and 0.78. My question is if 0.78 is significantly greater than 0.72. I'm using rcorrp.cens. I cannot find the U statistics in the output of the function. This is the output of the help example: > x1 <- rnorm(400) > x2 <- x1 + rnorm(400) > d.time <- rexp(400) + (x1 - min(x1)) > cens <- runif(400,.5,2) > death
2005 Sep 02
1
C-index : typical values
I am doing some coxPH model fitting and would like to have some idea about how good the fits are. Someone suggested to use Frank Harrell's C-index measure. As I understand it, a C-index > 0.5 indicates a useful model. I am probably making an error here because I am getting values less than 0.5 on real datasets. Can someone tell me where I am going wrong please ? Here is an example using
2008 Aug 11
1
Unexpected parameter problem using rsaga.geoprocessor() {RSAGA}
Hello, I discovered SAGA, an interesting free GIS, a few days ago and now, I would like to use it from within R 2.6.2 using the RSAGA package. I read the documentation for this package and thought that I understood it correctly for trying to call some of the SAGA modules. For getting the information on the usage of and arguments required by the SAGA command line "Import Binary Raw
2011 Feb 19
0
contrasting Somer's D from Design package
Dear R help, I am having a problem with the Design package and my problem is detailed here. I fit a cox model to my data and validate the Somer's Dxy using the Design package. (Because of computation time problem, i only try 10 bootstrap samples for the time being) This is the model without stratification: > library(Design) >
2012 Apr 08
0
Need help interpreting output from rcorrp.cens with Cox regression
Dear R-listers, I am an MD and clinical epidemiologist developing a measure of comorbidity severity for patients with liver disease. Having developed my comorbidity score as the linear predictor from a Cox regression model I want to compare the discriminative ability of my comorbidity measure with the "old" comorbidity measure, Charlson's Comorbidity Index. I have nearly 10,000
2012 Aug 17
0
REPOST: Need help interpreting output from rcorrp.cens with Cox regression
I am reposting my message from April 8th because I never received a response to the original post: Dear R-listers, I am an MD and clinical epidemiologist developing a measure of comorbidity severity for patients with liver disease. Having developed my comorbidity score as the linear predictor from a Cox regression model I want to compare the discriminative ability of my comorbidity measure with
2002 Jun 20
1
Bug in printing symbolic derivative (PR#1697)
A colleague pointed out the following error in D(): f <- expression(exp(-2*x*y)) Dx <- D(f, 'x') Dy <- D(f,'y') Dxy <- D(Dx, 'y') Dyx <- D(Dy, 'x') Then > Dx # this is right -exp(-2 * x * y) * (2 * y) > Dy # this is right exp(-2 * x * y) * (-2 * x) > Dxy # this is wrong in the sign of the second term!!! -exp(-2 * x * y) *
2009 May 13
1
Nagelkerkes R2N
Hello All, as I?m new to R and survival analysis, I?ve got a question about the Design::validate function: My Code: cox <- cph(Surv(t,status) ~ var1 + var2 + var3, data=data, x=TRUE, y=TRUE, surv=TRUE) cox.val <- validate(cox, B=10, dxy=TRUE, pr=TRUE); My output (cox.val): index.orig training test Dxy -0.3639222921368090891
2010 Dec 09
1
error in lrm( )
Dear Sir or Madam? I am a doctor of urology,and I am engaged in developing a nomogram of bladder cancer. May I ask for your help on below issue? I set up a dataset which include 317 cases. I got the Binary Logistic Regression model by SPSS.And then I try to reconstruct the model ?lrm(RECU~Complication+T.Num+T.Grade+Year+TS)? by R-Project,and try to internal validate the model through
2019 Oct 31
2
head.matrix can return 1000s of columns -- limit to n or add new argument?
...> > else > > dimsx <- length(x) > > > ## this returns a list of vectors of indices in each > > ## dimension, regardless of length of the the n > > ## argument > > sel <- lapply(seq_along(dimsx), function(i) { > > dxi <- dimsx[i] > > ## select all indices (full dim) if not specified > > ni <- if(length(n) >= i) n[i] else dxi > > ## handle negative ns > > ni <- if (ni < 0L) max(dxi + ni, 0L) else min(ni, dxi) > > seq.int(to = dxi, length.out =...
2009 Jul 15
0
Nagelkerkes R2N
I am interested Andrea is whether you ever established why your R2 was 1. I have had a similar situation previously. My main issue though, which I'd be v grateful for advice on, is why I am obtaining such negative values -0.3 for Somers Dxy using validate.cph from the Design package given my value of Nagelkerke R2 is not so low 13.2%. I have this output when fitting 6 variables all with