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...etrics (e.g., see Bollen and Lennox 1991; Edwards and Bagozzi 2000), and was a driving force behind the development of graphical models for causal analysis (Spirtes et al. 2000; Pearl 2000). By representing relationships between variables (e.g., correlations) as weighted edges important structures can be detected that are hard to extract by other means. In general, qgraph enables the researcher to represent complex statistical patterns in clear pictures, without the need for data reduction methods. qgraph was developed in the context of network approaches to psychometrics (Cramer et al. 2010; Borsboom 2008; Schmittmann et al. 2012), in which theoretical constructs in psychology are hypothesized to be networks of causally coupled variables. In particular, qgraph automates the production of graphs such as those proposed in Cramer et al. (2010). However, the techniques in the package have also proved useful as a more general tool for visualizing data, and include methods to visualize output from several psychometric packages like sem (Fox 2006; Fox et al. 2012) and lavaan (Rosseel 2012). A number of R packages can be used for the visualization and analysis of networks, e.g., network (Butts et al. ...

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...ne.org 2 April 2013 | Volume 8 | Issue 4 | e60188 In our case, Ypdtj represents the measurement for person px (p=1,2,…,129) at day d (d = 1,2,…,12) and time t of the j-th criterion variable. Equation =-=(1)-=- represents the multiple regression of a single variable at time point t on all other variables at time point t{1. Because there are six variables, there are six such regression equations – one for ea...

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...t predispose towards comorbidity [6–8]. However, a limitation of this methodology is that symptoms are viewed as passive indicators of ‘‘latent’’ conditions (disorders) that do the actual causal work =-=[9,10]-=-. Comorbidity is then suggested to arise from a root cause that is shared by two or more latent disorders. For instance, shared genes or a general predisposition towards negative affect have been put ...

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... variable model. According to this model, symptoms of a given disorder are assumed to share an essential property; namely, their causal dependence on a latent variable, from which all symptoms arise (=-=Borsboom, 2008-=-; Kendler et al. 2011). In this perspective, symptoms experienced by patients are merely effects of the relevant latent variable (in this case depression). Standard models assume the symptoms to be st...

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...cations about measurement in psychology bears witnesssto a profound crisis at the heart of the discipline (e.g., Borsboom, 2003; Cliff, 1992;sDooremalen & Borsboom, 2010; Essex & Smythe, 1999; Haig & =-=Borsboom, 2008-=-;sHood, 2009; Johnson, 1936; Lumsden, 1976; Michell, 1990, 1997, 1999, 2000, 2003a,sCorresponding author: Stéphane Vautier, Octogone, University of Toulouse-Le Mirail, 5 allées Antonio Machado, 31058 ...

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... in clinical psychology and psychiatry [2,3]. In practice, comorbidity is often investigated by analyzing the association between composite measures defined on two sets of items (i.e., a correlation between total scores on checklists) or between two diagnoses. This methodology has yielded important insights into which disorders co-occur more frequently than chance [1,4,5] and into risk factors that predispose towards comorbidity [6–8]. However, a limitation of this methodology is that symptoms are viewed as passive indicators of ‘‘latent’’ conditions (disorders) that do the actual causal work [9,10]. Comorbidity is then suggested to arise from a root cause that is shared by two or more latent disorders. For instance, shared genes or a general predisposition towards negative affect have been put forward as common causes of comorbidity between Major Depressive Episode (MDE) and Generalized Anxiety Disorder (GAD; [11,12]). In clinical psychology and psychiatry, however, symptoms are unlikely to be merely passive psychometric indicators of latent conditions; rather, they indicate properties with autonomous causal relevance. That is, when symptoms arise, they can cause other symptoms on their...

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...SCL-90 Depression scale is a symptom measure of depression. Depression as a theoretical construct is related to observed indicators, both within the diagnostic and dimensional diagnostic perspective (=-=Borsboom, 2008-=-). In this paper, we used the term ‘Depression’ as the label of the continuous latent underlying variable being reflected by the SCL-90 symptom indicators. Even if these symptom indicators would be re...

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...pproach, a psychiatric disorder is conceptualized assbeing characterized by a constellation of symptoms, inscontrast to a single underlying “essence” or constructsfrom which all other symptoms arise (=-=Borsboom, 2008-=-;sKendler, Zachar, & Craver, 2011). Thus, psychiatric disorders like MDD are not necessarily best characterized bysdefining specific single traits (e.g., depressed mood) but,sinstead, by elucidating t...