We have seen that there are differences (variance) in the mouth mean values (in statistic language: random intercepts).

It is also possible to find differences (variance) between the mouths in teeth level associations within the mouths (in statistic language: random slopes). E.g., the tooth association between tooth colour and tooth health status may be different in different mouths.

OBSERVE that in this very example the differences between the mouths are larger when the tooth colour value (B) is larger compared to (A). That is the mouth differences (variance) are a function of the tooth colour value.