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R1. Introduction
In our target article, we have proposed a network view of mental disorders, in which systematic covariation between symptoms is explained by direct relations between the symptoms themselves. The approach breaks radically with the dominant doctrine, in which disorders are considered to be common causes of their symptoms (i.e., the latent variable perspective). We were pleased to see that many commentators view the network approach as a potential substantive theory of mental disorders. Given the varied set of responses, many of which proposed worthwhile empirical research suggestions and theoretical extensions of the approach, we have fortunately succeeded in bringing together researchers from different fields to reconsider what disorders are and how we should investigate them.
One of the most surprising and noteworthy facts about the present set of commentaries concerns what they do not contain: Very few commentators attempt to defend the received view that underlies many current approaches to psychopathology: that is, the latent variable perspective. We take this to imply that the time is ripe for a change of perspective. In addition, the comments have strengthened our conviction that, with the necessary refinements and extensions, “‘inference to the best explanation” could ultimately lead us to the network approach as the substantive theory of mental disorders (Haig 2009). Certainly, Rothenberger, Banaschewski, Becker, & Roessner (Rothenberger et al.) argue that the network approach is complex with its “manifold interactions between symptoms,” but we agree with them even more that this reflects reality. And as we will argue here, complex realities require complex theories.
In this response, we discuss the most important extensions, refinements, investigative tools, and objections voiced by the commentators according to the following themes. First, several commentators argued that network models can and necessarily must include latent variables (e.g., Haig & Vertue; McFarland & Malta). In section R2, we explain why some relations qualify for such a measurement model – and are thus likely to be incorporated into a network model – while others do not (e.g., depression as common cause of a cluster of symptoms). Other commentators provided excellent suggestions for refinement of the network model in order to include genetic, neurological, and cognitive levels of explanation (e.g., Rubinsten & Henik; Yordanova, Kolev, Kirov,...