[R] Plotting interactions from lme with ggplot

[dadrivr]

Could somebody look at this?  I'm new to ggplot, so any help would be greatly
appreciated.  I provided an example to facilitate.  Thanks!


dadrivr wrote
> 
> I'm fitting a lme growth curve model with two predictors and their
> interaction as predictors. The multilevel model is nested so that level 1
> is time within the individual, and level 2 is the individual.  I would
> like to plot the mean group-level trajectories at plus and minus 1 SD from
> the mean of the main effects composing the interaction term.  Thus, the
> plot should have 4 lines (mean trajectories) representing all combinations
> of the two predictors (where LO = -1sd from its mean, and HI = +1sd from
> its mean):
> -LO predictor, LO moderator
> -LO predictor, HI moderator
> -HI predictor, LO moderator
> -HI predictor, HI moderator
> 
> They are growth curves, so the plot should have 'time' on the x-axis and
> 'outcome' on the y-axis.  Here's a sample model:
> 
> library(nlme)
> 
> set.seed(123)
> 
> dataset <- NULL
> dataset$id <- rep(1:100, each=10)
> dataset$time <- rep(1:10,100)
> dataset$outcome <- rnorm(1000, mean=100, sd=15)
> dataset$predictor <- rnorm(1000, mean=10, sd=3)
> dataset$moderator <- rnorm(1000, mean=5, sd=2)
> 
> dataset <- as.data.frame(dataset)
> dataset[sample(1:1000, 400, replace=F),"outcome"] <- NA
> dataset[sample(1:1000, 400, replace=F),"predictor"] <- NA
> dataset[sample(1:1000, 400, replace=F),"moderator"] <- NA
> 
> model <- lme(outcome~ time + predictor + moderator + predictor*moderator,
> random=~1 + time + predictor|id, data=dataset, na.action=na.omit)
> 
> How can I plot the interaction on the mean group-level trajectories using
> ggplot?  Thanks in advance!
> 


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