Networks vs latent variables Eiko Fried SEM 2, UvA, 22.05.2017

Why do certain things co-occur Flock of birds: https://www.youtube.com/watch?v=DmO4Ellgmd0

What are psychological constructs Intelligence Personality Mental disorders

What are psychological constructs Answering this question requires both a theory and the appropriate statistical model. These have often been mixed up.

Theoretical models PCs are: Natural kinds: categories discovered Elements Social kinds: categories produced Complex kinds: homeostatic property clusters Species Practical kinds: categories should be useful, not real SES 79;

Statistical models PCs can be modeled as: Reflective latent variable models Formative latent variable models Network models 79;

Statistical models 1 Reflective latent variable models; implied by natural kinds Schizophrenia, intelligence, extraversion While natural kinds imply reflective model, opposite not true (e.g. rich) Can in principle be discovered; assumes realist ontology

Statistical models 1 Can in principle be discovered (latent cause) Assumes realist ontology (“depression = brain disorder” is not just metaphor) Can in principle be discovered; assumes realist ontology

Statistical models 2 Formative latent variable models SES

Statistical models 3 Network model: implied model for complex kinds Intelligence, personality, mental disorders

Statistical models 3 Network model: implied model for complex kinds Intelligence, personality, mental disorders

Why symptoms cluster in syndromes

Mental disorders Why do researchers (implicitly) think about them as natural kinds Why do researchers predominantly use factor models to study them

Natural kinds Robert Koch, 1905: discovery that specific diseases have specific causative agents (tuberculosis & syphilis) Diseases understood as natural kinds Measles: infection of the respiratory system caused by a specific virus, accompanied by specific symptoms like red eyes, fever, generalized rash, and Koplik's spots Gold: atomic number 79, and everything with this atomic number is gold

Natural kinds 1910: discovery of syphilitic bacteria in brains of deceased patients diagnosed with "general paralysis of the insane" Neuropsychiatric syndrome of late-stage syphilis Clear "essence" identified for a mental disorder Disease model applied to the rest of medicine, including psychiatry

Mental disorders as natural kinds The assumption of mental disorders as natural kinds has been present throughout the history of psychiatry Gerald Klerman, chief of the US national mental health agency, 1978: "there is a boundary between the normal and the sick" "there are discrete mental disorders" Aim of developing specific treatments for particular disorders, and of finding specific underlying biological abnormalities Diagnoses are categorical (you have schizophrenia or you do not)

Common cause framework Derived from the notion of natural kinds Disorders itself are latent—we cannot observe measles directly M

Common cause framework Derived from the notion of natural kinds Disorders itself are latent—we cannot observe measles directly We can only observe the symptoms of measles We can use symptoms to indicate the presence of measles s1 M s2 s3

Common cause framework Derived from the notion of natural kinds Disorders itself are latent—we cannot observe measles directly We can only observe the symptoms of measles We can use symptoms to indicate the presence of measles This works because measles causes measles symptoms s1 M s2 s3

Common cause framework The CC framework is responsible for symptom checklists in the rest of medicine and psychiatry We use symptom lists to determine the presence of an underlying disease The CC framework explains why symptoms cluster: they have the same causal origin Fever, generalized rash, Koplik's spots  measles! s1 s2 s3 M

Common cause framework What does this mean for symptoms? Symptoms are equivalent & interchangeable indicators of underlying disease ("assumption of symptom equivalence") Symptom number, not symptom nature is relevant Symptoms are "locally independent"; since they are derived from the same common cause, their correlations are spurious

Network perspective Common cause: symptoms cluster because of a shared origin Network: symptoms cluster bc they influence each other

Network perspective Symptoms as separate entities that differ in important aspects More than interchangeable indicators of underlying disorder

But it’s more complicated than that Common causes for some sets of symptoms? (https://osf.io/mh3cf/) Trauma → PTSD symptoms Particular life events → particular depression symptoms

But it’s more complicated than that Common causes for some sets of symptoms? (https://osf.io/mh3cf/) Trauma → PTSD symptoms Particular life events → particular depression symptoms

Conclusion Think about theory before you move on to modeling, and consider what theory is implied by your model Distinguish theoretical from statistical model Network and latent variable models offer different insights and are complimentary, not competing The network theory (e.g. of mental disorders) and the common cause theory are competing, and they cannot both be fully true at the same time (although both can be true to a certain degree simultaneously; e.g. PTSD onset could be a common cause, PTSD maintenance a network)

References General Fried, E. I. (2017). What are psychological constructs? On the nature and statistical modeling of emotions, intelligence, personality traits and mental disorders. Health Psychology Review, 11(2), 130–134. http://doi.org/10.1080/17437199.2017.1306718 Personality Mõttus, R., & Allerhand, M. (2017). Why do traits come together? The underlying trait and network approaches. In V. Zeigler-Hill & T. Shackelford (Eds.), SAGE handbook of personality and individual differences: Volume 1. The science of personality and individual differences (pp. 1–22). London: SAGE. Intelligence van der Maas, H. L. J., Kan, K., Marsman, M., & Stevenson, C. E. (2017). Network Models for Cognitive Development and Intelligence, (January), 1–14. http://doi.org/10.20944/preprints201701.0107.v1

References Psychopathology Borsboom, D. (2017). A network theory of mental disorders. World Psychiatry, 16. Fried, E. I., van Borkulo, C. D., Cramer, A. O. J., Boschloo, L., Schoevers, R. A., & Borsboom, D. (2016). Mental disorders as networks of problems: a review of recent insights. Social Psychiatry and Psychiatric Epidemiology, 1, 1–32. Cramer, A. O. J., Waldorp, L. J., van der Maas, H. L. J., & Borsboom, D. (2010). Comorbidity: a network perspective. The Behavioral and Brain Sciences, 33(2–3), 137–50. http://doi.org/10.1017/S0140525X09991567

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Psychological Dynamics

Networks!