We cannot learn the true explanatory factors from only observed dataThere is a latent space, ZZZ, which contains enough structure to sufficiently represent XXX where Function f=d⋅ef=d\cdot ef=d⋅e where e:X→Ze:X\rightarrow Ze:X→Z and d:Z→Xd:Z\rightarrow Xd:Z→X직접적으로 관찰되거나 측정이 되지 않는 변수관측변수에 의해 간접적으로 통계 측정을 수행