The omni-presence of latent variables

Since this book is about latent variable models it is natural to begin with a discussion of the meaning of the concept ‘latent variable’. Depending on the context, latent variables have been defined in different ways, some of which will be briefly described in this chapter, although we generally find the definitions too narrow (see also Bollen, 2002). In this book we simply define a latent variable as a random variable whose realizations are hidden from us. This is in contrast to manifest variables where the realizations are observed.