Statistics plays an important role in the professional expertise of a psychologist. It is a necessity for a psychologist to possess at least a basic understanding of statistics in order to comply with the ethical duty of competence, even if they do not use statistics in their daily work. Without such an understanding, a psychologist is not able to comprehend a large share of information which is critical in this professional field, does not understand the basics of obtaining data and processing it to get psychological knowledge, and cannot properly read and understand psychological research (Coolican, 2013).
Without the basic knowledge of statistics, a psychologist will be unable to understand a significant portion of psychological information, such as the likelihood of occurrence of certain psychological conditions. They will not be able to help their customers and provide even basic consultancy if it requires the understanding of numerical data.
A psychologist without any knowledge of statistics will also not understand the basic principles behind a large share of data processing in psychology, which means they will be unable to critically read it, and will have to simply believe that the data and conclusions are correct. Furthermore, they may often misinterpret data and draw wrong conclusions about it, leading to serious professional mistakes.
An example of a situation which necessitates the knowledge of statistics can be provided if the article by Anderson and Bushman (2001) is considered. The authors compute the Pearson’s correlation coefficient between the time one plays computer games and different measures of their aggression. The authors obtain correlation coefficients ranging from -.16 to.27, on which basis they state that “these results clearly support the hypothesis that exposure to violent video games poses a public-health threat” (Anderson & Bushman, 2001, p. 358), and give other similar claims. It appears likely that a reader without basic knowledge of statistics will think that, according to the article, computer games cause violence, whereas the correct conclusions from the article should be much weaker.
Therefore, a psychologist needs to have at least a basic knowledge of statistics if they are to be a competent professional.
References
Anderson, C. A., & Bushman, B. J. (2001). Effects of violent video games on aggressive behavior, aggressive cognition, aggressive affect, physiological arousal, and prosocial behavior: A meta-analytic review of the scientific literature. Psychological Science, 12(5), 353-359.
Coolican, H. (2013). Research methods and statistics in psychology (5th ed.). New York, NY: Routledge.