Fitting Psychological Development Curves Using Polynomial Equations: Based on Standardized Data from the 2020 Edition of the Kyoto Scale of Psychological Development

Abstract

This study attempted to represent psychological development curves using polynomial equations. We utilized standardized data from the 2020 edition of the Kyoto Scale of Psychological Development to specify these equations. Using the least squares method, we calculated equations from the first to the sixth degrees. The results indicated no difference in the fit of the psychological development curve at the third degree and beyond in terms of coefficients of agreement. Further, specifying the psychological development curve as a third-degree equation was found to be favorable. Additionally, the study inferred that individuals' rate of development varies from birth to adulthood; however, the speed of development gradually decreases with increasing age.

【Research Impact】

The Kyoto Scale of Psychological Development is a standardized scale widely used in Japan. This study investigated the representation of the psychological development curve using polynomial equations based on standardized data from the 2020 edition of the scale. Notably, this scale exhibited social significance because it can serve as an index of psychological development.