The synthetic estimation approach relies on the assumption that the relationship between variables at one level of analysis is similar at a different level of analysis, which is certainly not ideal. Nonetheless, whereas researchers often simply impute values from the larger units to the smaller units assuming homogeneity within the larger units, the synthetic estimation approach is more principled in attempting to build a model to predict such values.

Boessen, A., & Hipp, J. R. (2015). Close‐ups and the scale of ecology: Land uses and the geography of social context and crime. Criminology, 53(3), 399-426. doi:10.1111/1745-9125.12074