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Psychometrics builds on the fundamental premise that psychological attributes are unobservable and need to be inferred from observable behavior. Consequently, psychometric procedures consist primarily in applying latent variable modeling, which statistically relates latent variables to manifest variables. However, latent variable modeling falls short of providing a theoretically sound definition of psychological attributes. Whereas in a pragmatic interpretation of latent variable modeling latent variables cannot represent psychological attributes at all, a realist interpretation of latent variable modeling implies that latent variables are empty placeholders for unknown attributes. The authors argue that psychological attributes can only be identified if they are defined within the context of substantive formal theory. Building on the structuralist view of scientific theories, they show that any successful application of such a theory necessarily produces specific values for the theoretical terms that are defined within the theory. Therefore, substantive formal theory is both necessary and sufficient for psychological measurement. [ABSTRACT FROM AUTHOR]

The role of depolarization in the inverse glucose-dependence of glucagon secretion was investigated by comparing the effects of KATP channel block and of high potassium. The secretion of glucagon and insulin by perifused mouse islets was simultaneously measured. Lowering glucose raised glucagon secretion before it decreased insulin secretion, suggesting an alpha cell–intrinsic signal recognition. Raising glucose affected glucagon and insulin secretion at the same time. However, depolarization by tolbutamide, gliclazide, or 15 mM KCl increased insulin secretion before the glucagon secretion receded. In contrast to the robust depolarizing effect of arginine and KCl (15 and 40 mM) on single alpha cells, tolbutamide was of variable efficacy. Only when applied before other depolarizing agents had tolbutamide a consistent depolarizing effect and regularly increased the cytosolic Ca2+ concentration. When tested on inside-out patches tolbutamide was as effective on alpha cells as on beta cells. In the presence of 1 µM clonidine, to separate insulinotropic from glucagonotropic effects, both 500 µM tolbutamide and 30 µM gliclazide increased glucagon secretion significantly, but transiently. The additional presence of 15 or 40 mM KCl in contrast led to a marked and lasting increase of the glucagon secretion. The glucagon secretion by SUR1 knockout islets was not increased by tolbutamide, whereas 40 mM KCl was of unchanged efficiency. In conclusion a strong and sustained depolarization is compatible with a marked and lasting glucagon secretion. KATP channel closure in alpha cells is less readily achieved than in beta cells, which may explain the moderate and transient glucagonotropic effect. [ABSTRACT FROM AUTHOR]