1. The Science of Each and Every Person:
The Enduring Problem of Intraindividual
Variance and Structure in Personality Psychology
Ian J. Davidson, MA
PhD Candidate
Psychology Department - History & Theory
York University

2. Science of the Individual?
Nomothetic
(Universal)
Individual Differences
(Interindividual)
Idiographic
(Individual)

3. The Perfect Cockpit Psychologist Ted Rose reminds us of this event.
1940s US Air Force Research.
Physical measurements of 4,063 pilots.
The perfect cockpit for the average pilot—
but the average pilot was no pilot in particular.

4. The Lamiell Critique
We are studying “persons-as-groups,” not “persons-as-persons.”
Only gaining knowledge about the spaces between persons.
Knowledge gained at interindividual level is erroneously
extended to individual and universal levels.

5. The Science of the Intraindividual
Borsboom and colleagues revisited problem of
Disjuncture between inter- and intra-individual levels.
Trait structure approach influenced by R.B. Cattell’s
methodological writings.
Is the FFM:
Locally Homogeneous?
Locally Heterogeneous?
Locally Irrelevant?
(Cattell, 1952)

6. Historical and Public Connectionss
The variety of new approaches to the intraindividual mirror the disciplinary splintering of personality theory. The intraindividual shares Lamiell’s vision in spirit, but shirks epistemological transgression. How do psychologists reconcile these innovations with their field’s effects on the public?

7. Selected References
Allik, J., Realo, A., Mottus, R., Borkenau, P., Kuppens, P., & Hrebickova, M. (2012). Person-Fit to the Five Factor Model of Personality. Swiss Journal of Psychology, 71(1), 35–45.
Allport, G. W. (1937). Personality: A psychological interpretation. H. Holt and Company.
Borkenau, P., & Ostendorf, F. (1998). The Big Five as States: How Useful Is the Five-Factor Model to Describe Intraindividual Variations over Time? Journal of Research in Personality, 32(2), 202–221.
Borsboom, D., Mellenbergh, G. J., & van Heerden, J. (2003). The theoretical status of latent variables. Psychological Review, 110(2), 203– X
Cervone, D. (2005). Personality Architecture: Within-Person Structures and Processes. Annual Review of Psychology, 56(1), 423–
Daniels, G. S. (1952). DTIC AD : THE “AVERAGE MAN” ? Defense Technical Information Center. Retrieved from
Eysenck, H. J. (1954). The science of personality: Nomothetic. Psychological Review, 61(5), 339–
Lamiell, J. T. (1987). The psychology of personality: An epistemological inquiry. New York, NY, US: Columbia University Press.

8. Selected References
Lamiell, J. T. (1997). Individuals and the differences between them. In R. Hogan, J. A. Johnson, & S. R. Briggs (Eds.), Handbook of personality psychology (pp. 117–141). San Diego, CA, US: Academic Press.
Lerner, R. M., & Murray, E. D. (2016). Finally! A Developmental Science that Privileges Development. Human Development, 59(6), 377–385.
McAdams, D. P. (2015). The Art and Science of Personality Development. New York: The Guilford Press.
Molenaar, P. C. M., & Campbell, C. G. (2009). The New Person-Specific Paradigm in Psychology. Current Directions in Psychological Science, 18(2), 112–
Molenaar, P. C. M., Sinclair, K. O., Rovine, M. J., Ram, N., & Corneal, S. E. (2009). Analyzing developmental processes on an individual level using nonstationary time series modeling. Developmental Psychology, 45(1), 260–271.
Pervin, L. A. (1989). Persons, situations, interactions: The history of a controversy and a discussion of theoretical models. Academy of Management Review, 14(3), 350–
Rose, T. (2016). The End of average: How we succeed in a world that values sameness. New York: HarperOne.

9. Thank you!