I'm looking at the relationship between income and scores on an instrument. Income is estimated by ZIP code. To account for nesting (i.e., people within the same ZIP code sharing an income), I've run a mixed model with ZIP as the random effect. There's a mean of 1.9 observations per ZIP. Is this too low to use a mixed model? Is there a minimum number of observations per group that's statistically sound?
Hierarchical linear modeling - minimum number of observations per group?
- Thread starter tess2
- Start date
- Tags hierarchical model mixed model
I am sure there are better people out there to answer this question, more knowledgeable, but yeah that seems like too few. To put it in perspective how much more variability can be explained by controlling for the second level. Do you think they have random intercepts and slopes? So with the levels you get averages at group level, so at times probably an average of 1 and 2 people.
A quick thing you can likely do is run the model with and without controlling for groupings and see if it makes any difference, controlling for groups also probably sucks up degrees of freedom.
A quick thing you can likely do is run the model with and without controlling for groupings and see if it makes any difference, controlling for groups also probably sucks up degrees of freedom.