1. Networks vs latent variables Eiko Fried
SEM 2, UvA,

2. Why do certain things co-occur
Flock of birds:

3. What are psychological constructs
Intelligence
Personality
Mental disorders

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

5. 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;

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

7. 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

8. 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

9. Statistical models 2
Formative latent variable models
SES

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

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

12. Why symptoms cluster in syndromes

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

14. 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

15. 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

16. 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)

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

18. 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

19. 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

20. 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

21. 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

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

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

24. But it’s more complicated than that
Common causes for some sets of symptoms? (
Trauma → PTSD symptoms
Particular life events → particular depression symptoms

25. But it’s more complicated than that
Common causes for some sets of symptoms? (
Trauma → PTSD symptoms
Particular life events → particular depression symptoms

26. 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)

27. 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.
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.

28. 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.

30. Psychological Dynamics

31. Networks!