To demonstrate that psychological variables can be assessed, give students a well-established psychological measure (e.g., Rubin's Love Scale [box 3.2], IQ test (see this link for discussing the history of intelligence testing), self-monitoring scale, empathy scale, hope scale, etc.) and then present evidence for its validity. Useful resources include:
Chlopan, B. E., McCain, M. L., Carbonell, J. L., &Hagen, R. L. (1985). Empathy: Review of available measures.
Journal of Personality and Social Psychology, 48, 635-653.
Rotter, J. B. (1990). Internal versus external controlof reinforcement: A case history of a variable. American
Psychologist,45, 489-493.
Simpson, J. A. & Gangestad, S. W. (1991).Individual differences in sociosexuality: Evidence for
convergent and discriminant validity. Journal of
Personality and Social Psychology, 60, 870-883.
Snyder, C. R., Harris, C., Anderson, J. R.,Holleran, S. A., Irving, L. M., Sigmon, S., Yoshinobu, L.,
Gigg, J., Langelle, C., & Harney, P. (1991). The will and the
ways: Development and validation of an individual-differences
measure of hope. Journal of Personality and Social Psychology, 60, 570-585.