To demonstrate that psychological variables can be assessed, give students a well-established psychological measure (e.g., Rubin's Love Scale [Table 5-5, p. 131], 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 control of 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 validationof an individual-differences measure of hope. Journal of Personality and Social Psychology,
60, 570-585.