Some guidelines for structural equation modelling in cognitive neuroscience: the case of Charlton et al.'s study on white matter integrity and cognitive ageing.

Charlton et al. (2008) (Charlton, R.A., Landua, S., Schiavone, F., Barrick, T.R., Clark, C.A., Markus, H.S., Morris, R.G.A., 2008. Structural equation modelling investigation of age-related variance in executive function and DTI-measured white matter change. Neurobiol. Aging 29, 1547-1555) presented a model that suggests a specific age-related effect of white matter integrity on working memory. We illustrate potential pitfalls of structural equation modelling by criticizing their model for (a) its neglect of latent variables, (b) its complexity, (c) its questionable causal assumptions, (d) the use of empirical model reduction, (e) the mix-up of theoretical perspectives, and (f) the failure to compare alternative models. We show that a more parsimonious model, based solely on the well-established general factor of cognitive ability, fits their data at least as well. Importantly, when modelled this way there is no support for a role of white matter integrity in cognitive aging in this sample, indicating that their conclusion is strongly dependent on how the data are analysed. We suggest that evidence from more conclusive study designs is needed.