random effects

  1. M

    random effects in mixed models

    Hello I am not very familiar with mixed models --- I have been reviewing the various tutorials on the web but still am not sure if/how to specify my model, even to start with. I have a relatively simple design: - two weight groups (non-random; normal/obese) -- randomized within each group to...
  2. T

    How to do survival analysis in SAS with interval censoring and random effects

    Hi, I am interested in using survival analysis methods on seed germination data. I have just started reading Allison's Survival analysis in SAS. Accelerated failure time analysis (using PROC LIFEREG) and Cox proportional hazards models using PROC PHREG seem promising, but I have a feeling...
  3. J

    Correct interpretation of Lmer output

    I have produced the following model lmer(TotalPayoff~PgvnD*Type+Type*Asym+PgvnD*Asym+Game*Type+Game*PgvnD+Game*Asym+(1|Subject)+(1|Pairing),REML=FALSE,data=table1)->m1 PgvnD=A percentage (numeric) Asym= a factor 0 or 1 Type=a factor 1 or 2 Game= a factor 1 or 2 from this model the terms...
  4. J

    Correct structuring of random effects?

    Hi I have produced a mixed effects model as follows; lmer(TotalPayoff~Type+Game+PgvnD*Asym+(1|Subject)+(1|Pairing),REML=FALSE,data=table1)- each pairing contains 2 subjects and each Subject is in 2 different pairings with different subjects. Have I structured the random effects in the...
  5. J

    Standard Deviation of Random effect is 0?

    have a model with two random effects lmer(TotalPayoff~Type+Game+PgvnD*Asym+(1|Subject)+(1|Pairing),REML=FALSE,data=table)->m1 each pairing contains 2 subjects and each Subject is in 2 different pairings with different subjects. For some reason the subject random effect has SD =0 I do not...
  6. J

    Fixed and Random Effects in Mixed Modeling

    Thank ahead of time for any help. I am analyzing time series data. Originally I was running Repeated Measures ANOVA and entering between subjects variables. This was providing significant and interesting results. However, there is missing data, and of course, RM-ANOVA deletes listwise. I was...
  7. K

    interpreting random effects

    I have have measured the trait frequency for a "mountain" associated allele across a number of sites and years. In my (glmer) model I have summarized the allele frequency by site and year as the dependent (binomial) variable and specified site and year as random effects. The fixed effects are...
  8. S

    Random effects estimator

    Hi, I don't quite understand what a random effects estimator actually does... I have individual data for 2 (not adjacent) years: Some individuals were asked twice (1000 people), some only in one year (500 people). Estimating a random effects estimator with STATA results in 1500...
  9. L

    modeling temporal variation

    Hi I have 6 years of patient-level data and I'm using a hierachical (2-level) regression model. Could anyone suggest ways to model the temporal change in hospital-level variation in patient outcomes, in a multilevel model ? So far, my approach has been to run the model on separate years of...
  10. S

    Panel Data Analysis, Help Urgently Needed! Fixed & Random effects, Fama MacBeth etc.

    Hi, I have the following panel dataset: 11 years of annual data with a total of 250 observations. The panel is highly unbalanced, in the beginning years only few observations, while the last years make up the most of the observations. For instance, in year 1 I have only 6 observations, while...
  11. J

    longitudinal mixed model troubles

    I have growth data for 5 time points. In my unconditional model the quadratic trend best fits the data (likelihood ratio test). However, the random effect for the quadratic term is not significant but the fixed effect is significant. I also have trouble when adding covariates - the g matrix is...
  12. S

    fixed or random factor for ANOVA

    I've had a discussion with a colleague over the proper way to analyse results of an experiment. We tested the performance of 6 subjects in a psychophysical task as a function of 3 factors: isi (3 levels) , ear (2 levels), and modality (2 levels). I won't go into details of what each factor...