I have a survey data in 15 countries. The questionaire included the student age, gender, body mass index(BMI, outcome), physical activity and dietary, ect. The country level included the average income level, low, high and medium.
I am very new in this model, just started to read and learn.
First of all, I want to confirm whether it is right to use the hierarchical linear model? Level 1 is student level. Level 2 is country level.
Secondly, I want to understand the relationship between multi-culture and BMI. The language may be used for the country level variable, but actually, almost all the countries have their own language, it is difficult to combine them. Any other reasonable variables could be considered?
Last but not least, any recommended books or links?