  In empirical studies, the data usually don't include all the variables of
interest in an economic model. This paper shows the identification of
unobserved variables in observations at the population level. When the
observables are distinct in each observation, there exists a function mapping
from the observables to the unobservables. Such a function guarantees the
uniqueness of the latent value in each observation. The key lies in the
identification of the joint distribution of observables and unobservables from
the distribution of observables. The joint distribution of observables and
unobservables then reveal the latent value in each observation. Three examples
of this result are discussed.
