In psychology, most of the concepts, theories, ideas etc. of interest refer to latent variables, where a latent variable is one that can't be observed directly. Instead, one has to find a manifest variable, which can be observed directly and which can be used as an indicator for the latent variable. Unless there is a perfect indicator (which usually there is not), the measurement of the latent variable contains an error. To estimate the error, latent variable modelling techniques like CFA or Item Response Theory (among others) have been developed.
Latent Variable Theory
Now, it is generally agreed upon that variables like age and gender are manifest. But what is it that makes the difference between a latent and a manifest variable? Borsboom (2008) explicates this difference. In his latent variable theory, the distinction depends on the certainty, with which an inference can be made from the observed data to the variable in question. In this sense, a variable like gender is manifest, because one can infer with certainty if a subject is male or female from his or her answer on a questionnaire. Note that this is possible, even though one has not actually observed the gender of that subject. Borsboom's account of latent variable theory also implies that the status of a variable as latent vs. manifest can change over time, if for example more information becomes accessible. But as long as a variable has proven to be manifest, it remains latent.
It seems to me, then, that pretty much every researcher in psychology should use latent variable modelling techniques, since most of the time it is not at all possible to infer something with certainty. However, this is clearly not the case. There are numerous published articles that use manifest variables and analyze the relationships between them without accounting for measurement error, thereby implicitly making the latent variable in question a manifest variable. (If anyone wants citations for this claim, I will happily provide them.)
Question: Under what circumstances is it defendable to use manifest instead of latent variables in psychological research, even if it is clear that the variables can only be measured with error?
Borsboom, D. (2008). Latent variable theory. Measurement: Interdisciplinary Research & Perspective, 6(1-2), 25-53. PDF