I understand that you would consider multilevel or hierarchical linear mixed effects model with your data are nested with multiple level and be grouped. However, I assume that the observation will belong to single group in the nested data.
However, if the there is a portion of observations would belong to multiple groups. But in general the data are nested with specific level. Can I consider the mixed effect model to control the unobserved effect from different level? Or I can only add two dummy variable as fixed effect from two different level and ignore the impact from the higher level?