nlme

  1. B

    Non linear mixed effects model and autocorrelation

    Hello everyone ! I am working on a non-linear statistical mixed effects model using package nlme in the R software.. The response variable is a cumulative flux of carbon dioxide, representing soil carbon mineralisation, during soils incubation at controlled temperature and humidity. The...
  2. D

    plot a subset of intervals after lmList

    Dear reader, I am a first timer here (and an R newbie), so please tell me if you need more information to answer the following question: I have grouped data on insurance premiums for 7 companies. I estimated 7 individual linear models using lmList of the nlme library. Afterwards I can plot...
  3. M

    Can I use gls if I don't need to use mixed models and var is not structured?

    I have a continuous variable that is related to a covariable linearly. I need to compare this relationship between months (24 months), but the dataset is very heterogeneous: the sample size is different (very) between months and the covariate range is also different between months, obviously...
  4. H

    nlme arguments explained

    Hi All, I'm trying to run an nlme on some data looking at the nonlinear response (in this case 'distance', but will also use for 'weight') of individuals ('possum') over time (repeated measures, recorded weekly for 12 weeks = 'week'). There were 3 different 'treatment' groups. Other factors...
  5. S

    [R - nlme] non-linear regression Michaelis-Menten model

    Hello, I am attempting to model Michaelis-Menten uptake kinetics to predict denitrification rates (response) across a gradient of nitrate loading (predictor) in four seasons (June, August, October, and December) using a mixed effects model. The basic models run well in the nls program in R and...
  6. C

    "getVarCov" in lme

    Is "getVarCov" of lme output gives variance-covariance of estimated "Standard Deviation" of random effects or variance-covariance of estimated "variance" of random effects . library(nlme) fm1 <- lme(distance ~ age, data = Orthodont) VarCorr(fm1) getVarCov(fm1) That is , VarCorr(fm1)...
  7. C

    Problem with nlme() convergence in a Monte Carlo simulation

    Hello. As part of a Monte Carlo simulation, I'm programming some model comparisons on generated data. The underlying relationship in the data is a two-parameter exponential curve (y=a*e^(bx)), and among the models being compared are hyperbolic (y=a/(1+bx)), and quadratic (y=b*(x-a)^2)...
  8. R

    Linear Mixed Model Analysis with multiple fixed factors

    Hellow, Here is a question on linear mixed model analysis for an intervention The study composed of two group of subjects who receive a DrugA versus Placebo and their Cholestrol and Sugars measured at baseline, six months and 12 months. So i did a simple analysis to detect the changes with...
  9. X

    How to report a non-significant main effect with significant contrasts (LME)

    Hi :wave:, Sorry for a lengthy first post, but I'm at my wits end :( I am using multilevel linear modelling with nlme's lme function to analyse a mixed design (2 categorical predictors, 1 a repeated measure with 5 levels, the other not repeated with 3 levels). From Andy Field's...