Psychology and DNA: Probability, Not Certainty

[sue_frantz]

I recently finished Sam Kean’s (2012),  The Violinist’s Thumb the history, the present, and the future of DNA research. Kean writes, “Genes don’t deal in certainties; they deal in probabilities.” I love that – and I’m using it the first day of Intro Psych next term: “Psychology doesn’t deal in certainties; it deals in probabilities.”

I already talk about correlations as probabilities. The stronger the correlation, the higher the probability that if you know one variable, you can predict the other variable.

In the learning chapter, it’s not unusual for a student to say, “I was spanked, and I turned out okay.” Now I can repeat, “psychology doesn’t deal in certainties; it deals in probabilities.” When children are spanked, it increases the probability of future behavioral problems (Gershoff, Sattler, & Ansari, 2017). It is not a certainty.

Whenever aggression comes up as a topic, a student will say, “I play first-person-shooter games, and I’ve never killed anybody.” Again, “psychology doesn’t deal in certainties; it deals in probabilities.” Playing violent video games increases the chances of being aggressive. Watching violent movies increases the chances of being aggressive. Listening to violent-themed music increases the chances of being aggressive. (List is not exhaustive.) The more of those factors that are present, the greater the probability of behaving aggressively (Anderson, C, Berkowitz, L, Donnerstein, E, Huesmann, L, Johnson, J, Linz, D, Malamuth, N, & Wartella, 2003). It is not a certainty.

A student says, “I was deprived of oxygen when I was being born, and I haven’t developed schizophrenia” (McNeil, Cantor-Graae, & Ismail, 2000). (Okay, I have never had a student say this, but I wanted one more example.) Being deprived of oxygen at birth increases the probability of developing schizophrenia. It is not a certainty.

Any time a student reports an experience that does not match what most in a research study experienced, I can say “Like genetics, psychology doesn’t deal in certainties; it deals in probabilities.”

References

Anderson, C, Berkowitz, L, Donnerstein, E, Huesmann, L, Johnson, J, Linz, D, Malamuth, N, & Wartella, E. (2003). The influence of media violence on youth: . Psychological Science In The Public Interest (Wiley-Blackwell), 4(3), 81–110. https://doi.org/10.1111/j.1529-1006.2003.pspi_1433.x

Gershoff, E. T., Sattler, K. M. P., & Ansari, A. (2017). Strengthening Causal Estimates for Links Between Spanking and Children’s Externalizing Behavior Problems. Psychological Science, 95679761772981. https://doi.org/10.1177/0956797617729816

Kean, S. (2012). The Violinist’s Thumb. New York City: Little, Brown, and Company.

McNeil, T. F., Cantor-Graae, E., & Ismail, B. (2000). Obstetric complications and congenital malformation in schizophrenia. In Brain Research Reviews (Vol. 31, pp. 166–178). https://doi.org/10.1016/S0165-0173(99)00034-X