COMING OF AGE: A TALE OF TWO MATURITIES

Abstract

All countries distinguish between minors and adults for various legal purposes. Recent U.S. Supreme Court cases concerning the legal status of juveniles have consulted psychological science to decide where to draw these boundaries. However, little is known about the robustness of the relevant research, because it has been conducted largely in the U.S. and other Western countries. To the extent that lawmakers look to research to guide their decisions, it is important to know how generalizable the scientific conclusions are. This dissertation examines two psychological phenomena relevant to legal questions about adolescent maturity: cognitive capacity, which undergirds logical thinking, and self-regulatory capacity, which comprises individuals’ ability to restrain themselves in the face of emotional, exciting, or risky stimuli. Age patterns of these constructs were assessed in 5,227 individuals (50.7% female), ages 10-30 (M = 17.05, SD = 5.91) from eleven countries. There were three primary aims of this work. First was to replicate previous research on age patterns in cognitive capacity within the U.S.-only sample. Second was to replicate previous research on age patterns in self-regulatory capacity within the U.S.-only sample. Third was to extend analyses to include the other ten countries in the sample, and evaluate to what degree age patterns found in the U.S. generalize to other parts of the world. I explored age patterns in the U.S. using a variety of statistical approaches, including analysis of variance, regression, and piecewise regression to better understand how these analyses shape our conclusions regarding the age of maturity of cognitive capacity and self-regulatory capacity. Age patterns found in the U.S. were consistent with past research. Specifically, whereas cognitive capacity reached adult levels around age 16, self-regulatory capacity generally continued to mature beyond age 18. When extending the analyses to the other ten countries, I found that generally cognitive capacity matured prior to self-regulatory capacity, but there were numerous deviations from this pattern. For instance, some countries evinced no discernible age pattern in one or both composites (e.g., Kenya or Jordan), while in others self-regulatory capacity reached adult levels earlier than or at the same age as cognitive capacity, inconsistent with hypotheses. In sum, juveniles may be capable of deliberative decision making by age 16, but even young adults may demonstrate “immature” decision making in arousing situations. It is therefore reasonable to have different age boundaries for different legal purposes, at least in the U.S.: one for matters in which cognitive capacity predominates, and a later one for matters in which self-regulatory capacity plays a substantial role. Whether and how these results ought to inform policy in other countries, however, is unclear.