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I have spent a large amount of time trying to figure out how to generate a desired plot, and was wondering if any one can help. The plot is to illustrate an interaction between 'time' and 'group' on a binary response variable, which increases faster over time for 'group 2' than 'group 1'. Below is a simplified version of what I need using simulated data. I have correctly got to the point of plotting a slope for each group (I think), but now want to plot a measure of confidence around each of these slopes.

#simulate 41 individuals, each occurring over a random number of days:
days.each<-sapply(sample(2:40,41,T),function(a)1:a)
thedata<-data.frame(day=unlist(days.each))

#add the individual id in:
thedata$id<-rep(1:41,sapply(days.each,length))

#9 of these individuals are in group 1, and 10 and in group 2:
thedata$group<-ifelse(thedata$id<20,1,2)

#with increasing 'day', the y increases. This relationship is stronger in individuals from group 2:
thedata$y<-(thedata$day*thedata$group)

#Also, some individuals have generally higher 'y' than others:
thedata$y<-thedata$y+rnorm(41,10,3)[thedata$id]

#the y is binomial:
thedata$y<-rbinom(nrow(thedata),1,thedata$y/max(thedata$y))

#change the group and id to class "factor"
thedata$id<-as.factor(thedata$id);thedata$group<-as.factor(thedata$group)

#run the full model:
library(lme4)
model <- glmer(formula=y ~ day*group+(1|id),family=binomial,data=thedata)


#to illustrate the interaction, plot one line for each group:
vals<-predict(model,re.form=NA,type ="response")

plot(y~day,data=thedata,type="n")
lines(sort(vals[thedata$group==1])~sort(thedata$day[thedata$group==1]),col="black")
lines(sort(vals[thedata$group==2])~sort(thedata$day[thedata$group==2]),col="purple")

#now add confidence around these slopes?

any help would be massively appreciated

edit: Previous questions were based on fitting confidence around linear mixed models with a single predictor. This question is concerning confidence for each value of x1 from a generalized linear mixed model with binomial error structure which includes two independent variables and the interaction between them. If anyone can demonstrate how something similar to the blue bands from Extract prediction band from lme fit could be added to my plot, that would be excellent.

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    see `Predictions and/or confidence (or prediction) intervals on predictions` in http://glmm.wikidot.com/faq. – EDi Mar 27 '15 at 14:07
  • possible duplicate of [Extract prediction band from lme fit](http://stackoverflow.com/questions/14358811/extract-prediction-band-from-lme-fit) – EDi Mar 27 '15 at 14:07
  • Hi @EDi, thank you for your suggestion. But, I don't think it is a duplicate, as the other question cannot be used to answer this one (at least not by someone like me). If you could, however, show why this is a duplicate, and exactly how the previous question could be used, that would be massively appreciated. – user3122539 Apr 01 '15 at 10:48

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