# Testing for the effect of an intervention when it is applied on a group of which each individual is measured

Suppose we have 500 students nested in 20 classes (different classrooms), 25 students per class

student<-factor(1:500)
class<-rep(LETTERS[1:20],each=25)


They all take a test.

score<-rnorm(500,mean=80,sd=5)


The model below would tell you about the average scores and variability among students and classes

library(lme4)
lmer(score~(1|class))


Suppose further that a random 10 of the classrooms were painted red the other 10 were painted blue.

redvblue<-rep(0:1,each=250)


Is this a reasonable way to test for the effect of redvblue on test scores? And if it is reasonable, is there a better way?

lmer(score~redvblue+(1|class))


I'm wondering whether I should be concerned that redvblue was applied at the classroom level rather than the student level.